diff --git a/web/src/lib/api/pullCompose.ts b/web/src/lib/api/pullCompose.ts
index 74cef72fa..349cb13c2 100644
--- a/web/src/lib/api/pullCompose.ts
+++ b/web/src/lib/api/pullCompose.ts
@@ -1,4 +1,17 @@
-import type { BranchEntry } from "./repo";
+import type { Did } from "@atcute/lexicons/syntax";
+import type { RepoInfo } from "$lib/components/repo/types";
+import { createBobbinClient } from "./client";
+import { branches as listBranches, gitTarget, type GitServiceConfig } from "./gitclient";
+import { listCommits, toMirrorCommitSummary } from "./gitmirror";
+import { listRepos } from "./records";
+import {
+	repoNameOf,
+	sortBranches,
+	toBranchSummary,
+	type BranchEntry,
+	type BranchSummary,
+	type CommitSummary
+} from "./repo";
 
 export type PullSource = "patch" | "branch" | "fork";
 
@@ -67,3 +80,143 @@ export const composeQuery = (selection: ComposeSelection): string => {
 	if (selection.source === "fork" && selection.fork) query.set("fork", selection.fork);
 	return query.toString();
 };
+
+const BRANCH_LIMIT = 500;
+const COMMIT_LIMIT = 100;
+
+// one of the viewer's forks, as the fork picker needs it
+export interface ForkOption {
+	uri: string;
+	repoDid: string;
+	name: string;
+	knot: string;
+}
+
+export interface ComposeData {
+	commits: CommitSummary[];
+	commitsError: string;
+	// `owner/repo` of the source repo, for the browse-at-commit links
+	sourceRepoPath: string;
+	branches: BranchSummary[];
+	sourceBranches: BranchEntry[];
+	forkBranches: BranchEntry[];
+	forks: ForkOption[];
+	source: PullSource;
+	sourceBranch: string;
+	targetBranch: string;
+	fork: string;
+	patch: string;
+	sourceRepoDid: string;
+	sourceKnot: string;
+	showDetails: boolean;
+	prefillError: string;
+}
+
+// the route load calls this for the active account, the component calls it
+// again client-side when the pick diverges since only the fork lane depends
+// on the identity
+export const loadCompose = async (args: {
+	config: GitServiceConfig;
+	repo: RepoInfo;
+	viewer: { did: string; handle: string } | null;
+	params: URLSearchParams;
+	fetch: typeof globalThis.fetch;
+}): Promise<ComposeData> => {
+	const { config, repo, viewer, params, fetch: fetchFn } = args;
+	const repoDid = repo.repoDid;
+	if (!repoDid) throw new Error("This repository has not been indexed yet");
+
+	const ctx = createBobbinClient({ serviceUrl: config.bobbinUrl, fetch: fetchFn });
+	const source: PullSource = parseSource(params.get("source")) ?? "branch";
+
+	const [branchList, forkList] = await Promise.all([
+		listBranches(gitTarget(config, repo, fetchFn), BRANCH_LIMIT)
+			.then((page) => page.branches ?? [])
+			.catch(() => [] as BranchEntry[]),
+		viewer
+			? listRepos(ctx, viewer.did, { limit: 100 })
+					.then((page) =>
+						page.items
+							// `source` is any uri: an at-uri means a fork, anything else is
+							// an import, same test the repo layout's resolveSource makes
+							.filter(
+								(item) =>
+									item.value.source?.startsWith("at://") && item.value.repoDid
+							)
+							.map((item): ForkOption => ({
+								uri: item.uri,
+								repoDid: item.value.repoDid as string,
+								name: repoNameOf(item),
+								knot: item.value.knot
+							}))
+					)
+					.catch(() => [] as ForkOption[])
+			: Promise.resolve([] as ForkOption[])
+	]);
+
+	let fork = params.get("fork") ?? "";
+	if (source === "fork" && !fork && forkList.length === 1) fork = forkList[0].repoDid;
+	const forkRepo = forkList.find((entry) => entry.repoDid === fork);
+
+	let prefillError = "";
+	let forkBranches: BranchEntry[] = [];
+	if (source === "fork" && forkRepo) {
+		try {
+			const page = await listBranches(
+				gitTarget(config, { uri: forkRepo.uri, repoDid: forkRepo.repoDid }, fetchFn),
+				BRANCH_LIMIT
+			);
+			forkBranches = sortBranchesByRecency(page.branches ?? []);
+		} catch (cause) {
+			prefillError = cause instanceof Error ? cause.message : String(cause);
+		}
+	}
+
+	const sourceBranches = sourceBranchChoices(branchList);
+	const targetBranch = defaultTargetBranch(branchList, params.get("targetBranch") ?? "");
+	const sourceBranch = defaultSourceBranch(
+		source,
+		params.get("sourceBranch") ?? "",
+		sourceBranches,
+		forkBranches
+	);
+
+	const sourceRepoDid = fork || repoDid;
+	const hasComparison = Boolean(sourceRepoDid && sourceBranch && targetBranch);
+
+	let commits: CommitSummary[] = [];
+	let commitsError = "";
+	if (hasComparison && source !== "patch") {
+		try {
+			const page = await listCommits(ctx, {
+				repo: sourceRepoDid as Did,
+				ranges: [`${targetBranch}..${sourceBranch}`],
+				limit: COMMIT_LIMIT
+			});
+			commits = page.commits.map(toMirrorCommitSummary);
+		} catch (cause) {
+			commitsError = cause instanceof Error ? cause.message : String(cause);
+		}
+	}
+
+	return {
+		commits,
+		commitsError,
+		sourceRepoPath: forkRepo
+			? `${viewer?.handle ?? repo.ownerHandle}/${forkRepo.name}`
+			: `${repo.ownerHandle}/${repo.name}`,
+		branches: sortBranches(branchList.map(toBranchSummary)),
+		sourceBranches,
+		forkBranches,
+		forks: forkList,
+		source,
+		sourceBranch,
+		targetBranch,
+		fork,
+		patch: params.get("patch") ?? "",
+		sourceRepoDid,
+		sourceKnot: forkRepo?.knot ?? repo.knot,
+		showDetails: hasComparison,
+		prefillError
+	};
+};
diff --git a/web/src/lib/auth.svelte.ts b/web/src/lib/auth.svelte.ts
index 2120955ad..ea64139d4 100644
--- a/web/src/lib/auth.svelte.ts
+++ b/web/src/lib/auth.svelte.ts
@@ -19,7 +19,7 @@ import {
 	listStoredSessions
 } from "@atcute/oauth-browser-client";
 import { getContext } from "svelte";
-import { SvelteURL, SvelteURLSearchParams } from "svelte/reactivity";
+import { SvelteMap, SvelteURL, SvelteURLSearchParams } from "svelte/reactivity";
 import oauthMetadata from "./oauth-client-metadata.json";
 import {
 	type AuthAccount,
@@ -94,12 +94,14 @@ export interface Auth {
 	readonly authenticating: boolean;
 	readonly currentUser: CurrentUser | null;
 	readonly accounts: AuthAccount[];
+	hasAccount(did: string): boolean;
 	bobbinUrl: string;
 	refresh(): Promise<void>;
 	signIn(identifier: string, returnTo?: string): Promise<void>;
 	addAccount(identifier: string, returnTo?: string): Promise<void>;
 	completeSignIn(): Promise<string>;
-	switchAccount(did: Did): Promise<void>;
+	switchAccount(did: Did, returnTo?: string): Promise<boolean>;
+	agentFor(did: Did): Promise<OAuthUserAgent>;
 	removeAccount(did: Did): Promise<void>;
 	signOut(): Promise<void>;
 	signOutAll(): Promise<void>;
@@ -204,6 +206,7 @@ export const createAuth = (
 			: { kind: "logged-out" }
 	);
 	let accounts = $state<AuthAccount[]>([]);
+	const otherAgents = new SvelteMap<Did, OAuthUserAgent>();
 
 	// merge atcute's stored sessions with persisted account metadata.
 	const syncAccounts = () => {
@@ -253,12 +256,19 @@ export const createAuth = (
 	const adoptSession = (session: OAuthSession) => {
 		const nextAgent = new OAuthUserAgent(session);
 		const did = nextAgent.sub as Did;
+		otherAgents.delete(did);
 		state = { kind: "profile-loading", agent: nextAgent, did };
 		const known = loadAccounts().find((account) => account.did === did);
 		persistActive(did, known?.handle ?? did);
 		void hydrateProfile(did, nextAgent);
 	};
 
+	const forgetSession = (did: Did) => {
+		otherAgents.delete(did);
+		deleteStoredSession(did);
+		saveAccounts(dropAccount(loadAccounts(), did));
+	};
+
 	const activate = async (did: Did): Promise<boolean> => {
 		try {
 			const session = await getSession(did);
@@ -266,8 +276,7 @@ export const createAuth = (
 			return true;
 		} catch (cause) {
 			if (isDeadSessionError(cause)) {
-				deleteStoredSession(did);
-				saveAccounts(dropAccount(loadAccounts(), did));
+				forgetSession(did);
 				return false;
 			}
 			state = failureState(errorMessage(cause));
@@ -275,6 +284,43 @@ export const createAuth = (
 		}
 	};
 
+	// allowStale would let a dead session through, the write then fails with the raw pds error
+	const agentFor = async (did: Did): Promise<OAuthUserAgent> => {
+		configure();
+		const active = currentAgent();
+		const cached = active?.sub === did ? active : (otherAgents.get(did) ?? null);
+		try {
+			if (cached) {
+				await cached.getSession();
+				return cached;
+			}
+			const agent = new OAuthUserAgent(await getSession(did));
+			otherAgents.set(did, agent);
+			return agent;
+		} catch (cause) {
+			if (!isDeadSessionError(cause)) throw cause;
+			const handle = accounts.find((account) => account.did === did)?.handle ?? did;
+			if (currentDid() === did) {
+				await removeAccount(did);
+			} else {
+				forgetSession(did);
+				syncAccounts();
+			}
+			if (browser) {
+				try {
+					await signIn(did, location.pathname + location.search);
+					// the page is navigating away, stay pending so the form keeps its spinner
+					return new Promise<OAuthUserAgent>(() => {});
+				} catch {
+					// fall through to the inline error
+				}
+			}
+			throw new Error(`${handle}'s session expired. Sign in again to act as them.`, {
+				cause
+			});
+		}
+	};
+
 	const refresh = async () => {
 		if (!browser) return;
 		configure();
@@ -353,19 +399,22 @@ export const createAuth = (
 		}
 	};
 
-	const switchAccount = async (did: Did) => {
-		if (!browser) return;
+	const switchAccount = async (did: Did, returnTo = "/") => {
+		if (!browser) return false;
 		configure();
-		if (!(await activate(did))) syncAccounts();
+		if (await activate(did)) return true;
+		syncAccounts();
+		await signIn(did, returnTo);
+		return false;
 	};
 
 	const removeAccount = async (did: Did) => {
 		if (!browser) return;
 		const wasActive = currentDid() === did;
 		try {
-			const activeAgent = currentAgent();
-			if (wasActive && activeAgent) {
-				await activeAgent.signOut();
+			const agent = wasActive ? currentAgent() : (otherAgents.get(did) ?? null);
+			if (agent) {
+				await agent.signOut();
 			} else {
 				deleteStoredSession(did);
 			}
@@ -373,6 +422,7 @@ export const createAuth = (
 			deleteStoredSession(did);
 		}
 
+		otherAgents.delete(did);
 		saveAccounts(dropAccount(loadAccounts(), did));
 		accounts = reconcileAccounts(listStoredSessions(), loadAccounts());
 
@@ -394,12 +444,9 @@ export const createAuth = (
 	};
 
 	const signOutAll = async () => {
-		try {
-			const activeAgent = currentAgent();
-			if (activeAgent) await activeAgent.signOut();
-		} catch {
-			// remove local session state below.
-		}
+		const agents = [currentAgent(), ...otherAgents.values()].filter((agent) => agent !== null);
+		await Promise.allSettled(agents.map((agent) => agent.signOut()));
+		otherAgents.clear();
 		if (browser) {
 			for (const did of listStoredSessions()) deleteStoredSession(did);
 		}
@@ -447,6 +494,8 @@ export const createAuth = (
 		get accounts() {
 			return accounts;
 		},
+		hasAccount: (did: string) => accounts.some((account) => account.did === did),
+		agentFor,
 		refresh,
 		signIn,
 		addAccount: signIn,
diff --git a/web/src/lib/auth.test.ts b/web/src/lib/auth.test.ts
new file mode 100644
index 000000000..39b93b75e
--- /dev/null
+++ b/web/src/lib/auth.test.ts
@@ -0,0 +1,110 @@
+import type { Did } from "@atcute/lexicons/syntax";
+import type { Session } from "@atcute/oauth-browser-client";
+import {
+	OAuthResponseError,
+	OAuthUserAgent,
+	TokenRefreshError,
+	deleteStoredSession,
+	getSession
+} from "@atcute/oauth-browser-client";
+import { type Mock, beforeEach, describe, expect, it, vi } from "vitest";
+import { createAuth } from "./auth.svelte";
+
+interface MockAgent {
+	sub: string;
+	getSession: Mock;
+}
+
+vi.mock("@atcute/oauth-browser-client", async (importOriginal) => {
+	const mod = await importOriginal<Record<string, unknown>>();
+	class MockOAuthUserAgent {
+		static instances: MockOAuthUserAgent[] = [];
+		readonly sub: string;
+		getSession = vi.fn(async () => this.session);
+		signOut = vi.fn(async () => {});
+		constructor(readonly session: { info: { sub: string } }) {
+			this.sub = session.info.sub;
+			MockOAuthUserAgent.instances.push(this);
+		}
+	}
+	return {
+		...mod,
+		OAuthUserAgent: MockOAuthUserAgent,
+		configureOAuth: vi.fn(),
+		createAuthorizationUrl: vi.fn(),
+		finalizeAuthorization: vi.fn(),
+		getSession: vi.fn(),
+		listStoredSessions: vi.fn(() => []),
+		deleteStoredSession: vi.fn()
+	};
+});
+
+// the vi.mock above swaps in a class that records its instances
+const MockedUserAgent = OAuthUserAgent as unknown as { instances: MockAgent[] };
+
+const mockedGetSession = vi.mocked(getSession);
+const mockedDeleteStoredSession = vi.mocked(deleteStoredSession);
+
+const alice = "did:plc:alice" as Did;
+const liveSession = (did: Did): Session => ({ info: { sub: did } }) as unknown as Session;
+
+beforeEach(() => {
+	vi.clearAllMocks();
+	MockedUserAgent.instances.length = 0;
+});
+
+describe("agentFor", () => {
+	it("returns a live agent and reuses it", async () => {
+		mockedGetSession.mockResolvedValue(liveSession(alice));
+		const auth = createAuth("http://127.0.0.1:1", null);
+
+		const agent = await auth.agentFor(alice);
+		expect(agent.sub).toBe(alice);
+		expect(await auth.agentFor(alice)).toBe(agent);
+		expect(mockedGetSession).toHaveBeenCalledTimes(1);
+		expect(mockedGetSession.mock.calls[0]).toEqual([alice]);
+		expect(MockedUserAgent.instances[0].getSession).toHaveBeenCalledTimes(1);
+	});
+
+	it("prunes a revoked session and throws a friendly error", async () => {
+		mockedGetSession.mockRejectedValue(new TokenRefreshError(alice, "session was revoked"));
+		const auth = createAuth("http://127.0.0.1:1", null);
+
+		await expect(auth.agentFor(alice)).rejects.toThrow(/session expired/);
+		expect(mockedDeleteStoredSession).toHaveBeenCalledWith(alice);
+	});
+
+	it("treats an invalid_token response from the token endpoint as dead", async () => {
+		mockedGetSession.mockRejectedValue(
+			new OAuthResponseError(new Response(null, { status: 400 }), {
+				error: "invalid_token",
+				error_description: '"exp" claim timestamp check failed'
+			})
+		);
+		const auth = createAuth("http://127.0.0.1:1", null);
+
+		await expect(auth.agentFor(alice)).rejects.toThrow(/session expired/);
+		expect(mockedDeleteStoredSession).toHaveBeenCalledWith(alice);
+	});
+
+	it("keeps the session on transient failures", async () => {
+		const cause = new TypeError("fetch failed");
+		mockedGetSession.mockRejectedValue(cause);
+		const auth = createAuth("http://127.0.0.1:1", null);
+
+		await expect(auth.agentFor(alice)).rejects.toBe(cause);
+		expect(mockedDeleteStoredSession).not.toHaveBeenCalled();
+	});
+
+	it("prunes a cached agent whose session died since it was minted", async () => {
+		mockedGetSession.mockResolvedValue(liveSession(alice));
+		const auth = createAuth("http://127.0.0.1:1", null);
+		await auth.agentFor(alice);
+
+		MockedUserAgent.instances[0].getSession.mockRejectedValue(
+			new TokenRefreshError(alice, "session was revoked")
+		);
+		await expect(auth.agentFor(alice)).rejects.toThrow(/session expired/);
+		expect(mockedDeleteStoredSession).toHaveBeenCalledWith(alice);
+	});
+});
diff --git a/web/src/lib/components/auth/AccountSelector.stories.svelte b/web/src/lib/components/auth/AccountSelector.stories.svelte
new file mode 100644
index 000000000..b3ec48796
--- /dev/null
+++ b/web/src/lib/components/auth/AccountSelector.stories.svelte
@@ -0,0 +1,46 @@
+<script module lang="ts">
+	import { defineMeta } from "@storybook/addon-svelte-csf";
+	import { expect, userEvent, waitFor, within } from "storybook/test";
+	import type { Did } from "@atcute/lexicons/syntax";
+	import type { AuthAccount } from "$lib/auth.svelte";
+	import AccountSelector from "./AccountSelector.svelte";
+
+	const accounts: AuthAccount[] = [
+		{ did: "did:plc:alice" as Did, handle: "alice.tangled.sh", addedAt: 1 },
+		{ did: "did:plc:bob" as Did, handle: "bob.tangled.sh", addedAt: 2 },
+		{ did: "did:plc:carol" as Did, handle: "carol.with.a.rather.long.handle", addedAt: 3 }
+	];
+
+	const { Story } = defineMeta({
+		title: "Auth/AccountSelector",
+		component: AccountSelector,
+		tags: ["autodocs"]
+	});
+</script>
+
+<script lang="ts">
+	let switched = $state<string>(accounts[0].did);
+</script>
+
+<Story name="One account" asChild>
+	<AccountSelector accounts={[accounts[0]]} value={accounts[0].did} label="Comment as" />
+</Story>
+
+<Story name="Disabled" asChild>
+	<AccountSelector {accounts} value={accounts[1].did} label="Comment as" disabled />
+</Story>
+
+<Story
+	name="Picking another account"
+	asChild
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		await userEvent.click(canvas.getByRole("button", { name: /comment as alice/i }));
+		await userEvent.click(await canvas.findByRole("menuitem", { name: /bob/i }));
+		await waitFor(() =>
+			expect(canvas.getByRole("button", { name: /comment as bob/i })).toBeVisible()
+		);
+	}}
+>
+	<AccountSelector {accounts} bind:value={switched} label="Comment as" />
+</Story>
diff --git a/web/src/lib/components/auth/AccountSelector.svelte b/web/src/lib/components/auth/AccountSelector.svelte
new file mode 100644
index 000000000..f2cac9bf2
--- /dev/null
+++ b/web/src/lib/components/auth/AccountSelector.svelte
@@ -0,0 +1,65 @@
+<script module lang="ts">
+	import { tv } from "tailwind-variants";
+
+	export const accountSelector = tv({
+		slots: {
+			trigger: "flex min-w-0 items-center gap-1.5 text-foreground-muted",
+			chevron: "size-3 shrink-0",
+			header: "px-2 py-1.5 typography-paragraph-small text-foreground-muted"
+		}
+	});
+</script>
+
+<script lang="ts">
+	import ChevronDown from "$icon/chevron-down";
+	import type { AuthAccount } from "$lib/auth.svelte";
+	import Dropdown from "$lib/components/ui/Dropdown.svelte";
+	import DropdownItem from "$lib/components/ui/DropdownItem.svelte";
+	import User from "$lib/components/ui/User.svelte";
+
+	interface Props {
+		accounts: readonly AuthAccount[];
+		value: string;
+		label?: string;
+		disabled?: boolean;
+		group?: string;
+		class?: string;
+	}
+
+	let {
+		accounts,
+		value = $bindable(),
+		label = "Post as",
+		disabled = false,
+		group,
+		class: className
+	}: Props = $props();
+
+	const selected = $derived(accounts.find((account) => account.did === value));
+	const others = $derived(accounts.filter((account) => account.did !== value));
+	const classes = accountSelector();
+</script>
+
+{#if selected && others.length > 0}
+	<Dropdown
+		{group}
+		{disabled}
+		size="small"
+		label={`${label} ${selected.handle}`}
+		class={className}
+	>
+		{#snippet trigger()}
+			<span class={classes.trigger()}>
+				<User did={selected.did} handle={selected.handle} size="small" class="min-w-0" />
+				<ChevronDown class={classes.chevron()} aria-hidden="true" />
+			</span>
+		{/snippet}
+
+		<div class={classes.header()}>{label}</div>
+		{#each others as account (account.did)}
+			<DropdownItem onclick={() => (value = account.did)}>
+				<User did={account.did} handle={account.handle} size="small" class="min-w-0" />
+			</DropdownItem>
+		{/each}
+	</Dropdown>
+{/if}
diff --git a/web/src/lib/components/comment/CommentBox.svelte b/web/src/lib/components/comment/CommentBox.svelte
index 48a2e62ea..fdd101ba2 100644
--- a/web/src/lib/components/comment/CommentBox.svelte
+++ b/web/src/lib/components/comment/CommentBox.svelte
@@ -67,7 +67,9 @@
 			<Avatar did={authorDid} handle={authorHandle} size="large" />
 		</div>
 		<div class="flex min-w-0 flex-1 flex-col gap-2">
-			<div class="flex flex-wrap items-center gap-1 typography-paragraph-small text-foreground-subtle">
+			<div
+				class="flex flex-wrap items-center gap-1 typography-paragraph-small text-foreground-subtle"
+			>
 				<span class="text-foreground-default">{authorHandle}</span>
 			</div>
 			{@render editor()}
diff --git a/web/src/lib/components/comment/CommentCard.svelte b/web/src/lib/components/comment/CommentCard.svelte
index ebea0fee0..e3c360084 100644
--- a/web/src/lib/components/comment/CommentCard.svelte
+++ b/web/src/lib/components/comment/CommentCard.svelte
@@ -1,5 +1,6 @@
 <script lang="ts">
 	import { resolve } from "$app/paths";
+	import type { Did } from "@atcute/lexicons/syntax";
 	import Pencil from "$icon/pencil";
 	import Trash2 from "$icon/trash-2";
 	import { deleteComment } from "$lib/api/comment";
@@ -60,7 +61,10 @@
 	const onReacted = (uri: string) => (kind: ReactionKind, rkey: string) => {
 		const viewer = currentUser;
 		if (!viewer) return;
-		setReactions(uri, upsertViewerReaction(reactionsByUri[uri] ?? [], kind, viewer.handle, rkey));
+		setReactions(
+			uri,
+			upsertViewerReaction(reactionsByUri[uri] ?? [], kind, viewer.handle, rkey)
+		);
 	};
 
 	const onUnreacted = (uri: string) => (kind: ReactionKind) => {
@@ -75,14 +79,14 @@
 	};
 
 	const deleteSelected = createAction(async (comment: CommentView) => {
-		const agent = auth?.agent;
-		if (!agent) return;
+		if (!auth) return;
+		const agent = await auth.agentFor(comment.authorDid as Did);
 		await deleteComment(agent, comment.rkey);
 		ondeleted?.(comment.uri);
 	});
 
 	const handleDelete = (comment: CommentView) => {
-		if (!auth?.agent || deleteSelected.loading) return;
+		if (deleteSelected.loading) return;
 		if (!confirm("Delete this comment? This cannot be undone.")) return;
 		void deleteSelected.run(comment);
 	};
@@ -99,7 +103,7 @@
 				onreacted={onReacted(comment.uri)}
 				onunreacted={onUnreacted(comment.uri)}
 			/>
-			{#if currentUser.did === comment.authorDid}
+			{#if auth?.hasAccount(comment.authorDid)}
 				<button
 					type="button"
 					aria-label="Edit comment"
@@ -111,7 +115,8 @@
 				<button
 					type="button"
 					aria-label="Delete comment"
-					disabled={deleteSelected.loading && deleteSelected.args?.[0].uri === comment.uri}
+					disabled={deleteSelected.loading &&
+						deleteSelected.args?.[0].uri === comment.uri}
 					class="cursor-pointer text-foreground-danger hover:text-foreground-danger-strong disabled:opacity-50"
 					onclick={() => handleDelete(comment)}
 				>
diff --git a/web/src/lib/components/comment/CommentEditor.stories.svelte b/web/src/lib/components/comment/CommentEditor.stories.svelte
index 1a21f63f9..bb3d8fa2d 100644
--- a/web/src/lib/components/comment/CommentEditor.stories.svelte
+++ b/web/src/lib/components/comment/CommentEditor.stories.svelte
@@ -4,7 +4,9 @@
 	import MessageSquarePlus from "$icon/message-square-plus";
 	import Pencil from "$icon/pencil";
 	import CommentEditor from "./CommentEditor.svelte";
-	import MockAuthProvider from "$lib/components/testing/MockAuthProvider.svelte";
+	import MockAuthProvider, {
+		mockAccounts
+	} from "$lib/components/testing/MockAuthProvider.svelte";
 	import {
 		sampleComments,
 		sampleMarkup,
@@ -25,6 +27,8 @@
 		oncancel: () => undefined
 	};
 
+	const storyAccounts = mockAccounts.slice(0, 2);
+
 	const { Story } = defineMeta({
 		title: "Comment/CommentEditor",
 		component: CommentEditor,
@@ -67,3 +71,63 @@
 		</MockAuthProvider>
 	{/snippet}
 </Story>
+
+<Story
+	name="Composing with several accounts"
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		await userEvent.click(canvas.getByRole("button", { name: /comment as alice/i }));
+		await userEvent.click(await canvas.findByRole("menuitem", { name: /bob/i }));
+		await waitFor(() =>
+			expect(canvas.getByRole("button", { name: /comment as bob/i })).toBeVisible()
+		);
+	}}
+>
+	{#snippet template(args)}
+		<MockAuthProvider accounts={storyAccounts}>
+			<CommentEditor {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
+
+<Story
+	name="Editing with several accounts"
+	args={editArgs}
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		expect(canvas.queryByRole("button", { name: /comment as/i })).toBeNull();
+		await waitFor(() => expect(canvas.getByRole("button", { name: "Save" })).toBeVisible());
+	}}
+>
+	{#snippet template(args)}
+		<MockAuthProvider accounts={storyAccounts}>
+			<CommentEditor {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
+
+<Story
+	name="Expired session for the picked account"
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		await userEvent.click(canvas.getByRole("button", { name: /comment as alice/i }));
+		await userEvent.click(await canvas.findByRole("menuitem", { name: /bob/i }));
+		await userEvent.type(canvas.getByPlaceholderText(/add to the discussion/i), "as bob");
+		await userEvent.click(canvas.getByRole("button", { name: "Comment" }));
+		await waitFor(() =>
+			expect(canvas.getByRole("alert")).toHaveTextContent(/session expired/i)
+		);
+		await waitFor(() =>
+			expect(canvas.getByRole("button", { name: /comment as alice/i })).toBeVisible()
+		);
+		await userEvent.click(canvas.getByRole("button", { name: /comment as alice/i }));
+		await waitFor(() => expect(canvas.getByRole("menuitem", { name: /carol/i })).toBeVisible());
+		expect(canvas.queryByRole("menuitem", { name: /bob/i })).toBeNull();
+	}}
+>
+	{#snippet template(args)}
+		<MockAuthProvider accounts={mockAccounts} expired={["did:plc:bob"]}>
+			<CommentEditor {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
diff --git a/web/src/lib/components/comment/CommentEditor.svelte b/web/src/lib/components/comment/CommentEditor.svelte
index 20005dd05..dc9fd072a 100644
--- a/web/src/lib/components/comment/CommentEditor.svelte
+++ b/web/src/lib/components/comment/CommentEditor.svelte
@@ -2,9 +2,11 @@
 	import { untrack, type Component } from "svelte";
 	import type { SvelteHTMLElements } from "svelte/elements";
 	import { now as tidNow } from "@atcute/tid";
+	import type { Did } from "@atcute/lexicons/syntax";
 	import X from "$icon/x";
 	import { putComment } from "$lib/api/comment";
 	import { getAuth } from "$lib/auth.svelte";
+	import AccountSelector from "$lib/components/auth/AccountSelector.svelte";
 	import Button from "$lib/components/ui/Button.svelte";
 	import ErrorAlert from "$lib/components/ui/Error.svelte";
 	import MarkdownEditor from "$lib/components/ui/MarkdownEditor.svelte";
@@ -60,15 +62,24 @@
 	}: Props = $props();
 
 	const auth = getAuth();
+	const accounts = $derived(auth?.accounts ?? []);
+
+	let picked = $state<string | null>(null);
+	const acting = $derived(
+		accounts.find((account) => account.did === picked) ?? {
+			did: authorDid,
+			handle: authorHandle
+		}
+	);
 
 	let body = $state(untrack(() => initialBody));
 	let tab = $state<"write" | "preview">("write");
 
 	const publish = createAction(async (event: SubmitEvent) => {
 		event.preventDefault();
-		const agent = auth.agent;
-		if (!agent || body.trim() === "") return;
+		if (!auth?.currentDid || body.trim() === "") return;
 		if (!subjectCid) throw new Error("Cannot comment: the subject record is missing a cid.");
+		const agent = await auth.agentFor(acting.did as Did);
 		const createdAtValue = createdAt ?? new Date().toISOString();
 		const targetRkey = rkey ?? tidNow();
 		const record: CommentRecord = {
@@ -89,8 +100,8 @@
 				uri: saved.uri,
 				cid: saved.cid,
 				rkey: targetRkey,
-				authorDid,
-				authorHandle,
+				authorDid: acting.did,
+				authorHandle: acting.handle,
 				createdAt: createdAtValue,
 				body,
 				bodyHtml
@@ -141,5 +152,15 @@
 				Cancel
 			</Button>
 		{/if}
+		{#if !rkey}
+			<AccountSelector
+				{accounts}
+				bind:value={() => acting.did, (did) => (picked = did)}
+				label="Comment as"
+				disabled={publish.loading}
+				group="comment-editor"
+				class="ml-auto"
+			/>
+		{/if}
 	</div>
 </form>
diff --git a/web/src/lib/components/repo/issues/IssueForm.stories.svelte b/web/src/lib/components/repo/issues/IssueForm.stories.svelte
index 6f4bdeafe..5d9cd8901 100644
--- a/web/src/lib/components/repo/issues/IssueForm.stories.svelte
+++ b/web/src/lib/components/repo/issues/IssueForm.stories.svelte
@@ -2,11 +2,15 @@
 	import { defineMeta } from "@storybook/addon-svelte-csf";
 	import { expect, userEvent, waitFor, within } from "storybook/test";
 	import IssueForm from "./IssueForm.svelte";
-	import MockAuthProvider from "$lib/components/testing/MockAuthProvider.svelte";
+	import MockAuthProvider, {
+		mockAccounts
+	} from "$lib/components/testing/MockAuthProvider.svelte";
 
 	// no-ops; submitting is inert here (needs an authed agent context)
 	const noop = () => undefined;
 
+	const storyAccounts = mockAccounts.slice(0, 2);
+
 	const { Story } = defineMeta({
 		title: "Repo/Issues/IssueForm",
 		component: IssueForm,
@@ -58,3 +62,42 @@
 		</MockAuthProvider>
 	{/snippet}
 </Story>
+
+<Story
+	name="Opening as another account"
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		await userEvent.click(canvas.getByRole("button", { name: /open as alice/i }));
+		await userEvent.click(await canvas.findByRole("menuitem", { name: /bob/i }));
+		await waitFor(() =>
+			expect(canvas.getByRole("button", { name: /open as bob/i })).toBeVisible()
+		);
+	}}
+>
+	{#snippet template(args)}
+		<MockAuthProvider accounts={storyAccounts}>
+			<IssueForm {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
+
+<Story
+	name="Editing has no picker"
+	args={{
+		mode: "edit",
+		authorDid: "did:plc:alice",
+		title: "Add a full trending repositories view",
+		body: "I'd like a `/trending` view."
+	}}
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		expect(canvas.queryByRole("button", { name: /open as/i })).toBeNull();
+		await waitFor(() => expect(canvas.getByRole("button", { name: "Save" })).toBeVisible());
+	}}
+>
+	{#snippet template(args)}
+		<MockAuthProvider accounts={storyAccounts}>
+			<IssueForm {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
diff --git a/web/src/lib/components/repo/issues/IssueForm.svelte b/web/src/lib/components/repo/issues/IssueForm.svelte
index ca80f9914..e04d62824 100644
--- a/web/src/lib/components/repo/issues/IssueForm.svelte
+++ b/web/src/lib/components/repo/issues/IssueForm.svelte
@@ -1,11 +1,13 @@
 <script lang="ts">
 	import { untrack } from "svelte";
 	import { now as tidNow } from "@atcute/tid";
+	import type { Did } from "@atcute/lexicons/syntax";
 	import CirclePlus from "$icon/circle-plus";
 	import Pencil from "$icon/pencil";
 	import X from "$icon/x";
 	import { putIssue } from "$lib/api/issue";
 	import { getAuth } from "$lib/auth.svelte";
+	import AccountSelector from "$lib/components/auth/AccountSelector.svelte";
 	import Button from "$lib/components/ui/Button.svelte";
 	import ErrorAlert from "$lib/components/ui/Error.svelte";
 	import Input from "$lib/components/ui/Input.svelte";
@@ -20,6 +22,7 @@
 		repoDid: string;
 		markup: MarkupContext;
 		mode?: "create" | "edit";
+		authorDid?: string;
 		rkey?: string;
 		createdAt?: string;
 		title?: string;
@@ -35,6 +38,7 @@
 		repoDid,
 		markup,
 		mode = "create",
+		authorDid,
 		rkey,
 		createdAt,
 		title: initialTitle = "",
@@ -47,6 +51,15 @@
 	}: Props = $props();
 
 	const auth = getAuth();
+	const accounts = $derived(auth?.accounts ?? []);
+
+	let picked = $state<string | null>(null);
+	const actingDid = $derived(
+		accounts.find((account) => account.did === picked)?.did ??
+			authorDid ??
+			auth?.currentDid ??
+			""
+	);
 
 	let title = $state(untrack(() => initialTitle));
 	let body = $state(untrack(() => initialBody));
@@ -55,12 +68,12 @@
 
 	const save = createAction(async (event: SubmitEvent) => {
 		event.preventDefault();
-		const agent = auth.agent;
-		if (!agent || title.trim() === "") return;
+		if (!auth?.currentDid || title.trim() === "") return;
 		if (submit) {
 			await submit({ title, body });
 			return;
 		}
+		const agent = await auth.agentFor(actingDid as Did);
 		const targetRkey = rkey ?? tidNow();
 		const record: IssueRecord = {
 			$type: "sh.tangled.repo.issue",
@@ -77,7 +90,9 @@
 
 <form onsubmit={save.run} class="flex flex-col gap-4">
 	<div class="flex flex-col gap-1.5">
-		<label for="issue-title" class="typography-paragraph-small text-foreground-default">Title</label>
+		<label for="issue-title" class="typography-paragraph-small text-foreground-default"
+			>Title</label
+		>
 		<Input id="issue-title" name="title" required bind:value={title} disabled={save.loading} />
 	</div>
 
@@ -98,6 +113,16 @@
 	<ErrorAlert label={save.error} />
 
 	<div class="flex items-center justify-end gap-2">
+		{#if mode === "create"}
+			<AccountSelector
+				{accounts}
+				bind:value={() => actingDid, (did) => (picked = did)}
+				label="Open as"
+				disabled={save.loading}
+				group="issue-form"
+				class="mr-auto"
+			/>
+		{/if}
 		<Button type="button" variant="default" icon={X} disabled={save.loading} onclick={oncancel}>
 			Cancel
 		</Button>
diff --git a/web/src/lib/components/repo/pulls/PullComment.svelte b/web/src/lib/components/repo/pulls/PullComment.svelte
index 5fd0c32c6..fd696c8ab 100644
--- a/web/src/lib/components/repo/pulls/PullComment.svelte
+++ b/web/src/lib/components/repo/pulls/PullComment.svelte
@@ -18,6 +18,7 @@
 	import TimeAgo from "$lib/components/ui/TimeAgo.svelte";
 	import type { CommentView, ThreadInput } from "$lib/components/comment/comments";
 	import type { MarkupContext } from "$lib/markup";
+	import type { Did } from "@atcute/lexicons/syntax";
 
 	// the appview's `fragments/comment/pullComment`: flat, no card, no replies.
 	// pull comments never thread — `submissionComments` just ranges over the round's
@@ -36,7 +37,7 @@
 
 	const auth = getAuth();
 	const currentUser = $derived(auth?.currentUser ?? null);
-	const isAuthor = $derived(currentUser?.did === comment.authorDid);
+	const isAuthor = $derived(auth?.hasAccount(comment.authorDid) ?? false);
 
 	let editing = $state(false);
 	let reactions = $derived(comment.reactions ?? []);
@@ -64,14 +65,14 @@
 	};
 
 	const remove = createAction(async () => {
-		const agent = auth?.agent;
-		if (!agent) return;
+		if (!auth) return;
+		const agent = await auth.agentFor(comment.authorDid as Did);
 		await deleteComment(agent, comment.rkey);
 		ondeleted?.(comment.uri);
 	});
 
 	const handleDelete = () => {
-		if (!auth?.agent || remove.loading) return;
+		if (!auth?.currentDid || remove.loading) return;
 		if (!confirm("Are you sure you want to delete your comment?")) return;
 		void remove.run();
 	};
@@ -82,7 +83,12 @@
 <div class="group/comment mx-auto -ml-4 flex w-full gap-2 py-4">
 	<div class="relative h-fit shrink-0">
 		<a href={profileHref(comment.authorHandle)} class="no-underline">
-			<Avatar handle={comment.authorHandle} did={comment.authorDid} size="full" class="size-8" />
+			<Avatar
+				handle={comment.authorHandle}
+				did={comment.authorDid}
+				size="full"
+				class="size-8"
+			/>
 		</a>
 	</div>
 	<div class="min-w-0 flex-1">
@@ -107,9 +113,16 @@
 				{/if}
 			</a>
 			{#if !comment.deleted}
-				<div class="ml-auto flex items-center gap-4 opacity-0 group-hover/comment:opacity-100">
+				<div
+					class="ml-auto flex items-center gap-4 opacity-0 group-hover/comment:opacity-100"
+				>
 					{#if currentUser}
-						<ReactionPicker subjectUri={comment.uri} {reacted} {onreacted} {onunreacted} />
+						<ReactionPicker
+							subjectUri={comment.uri}
+							{reacted}
+							{onreacted}
+							{onunreacted}
+						/>
 					{/if}
 					{#if isAuthor}
 						<button
@@ -165,9 +178,15 @@
 					<!-- eslint-disable-next-line svelte/no-at-html-tags -- sanitised in $lib/markup -->
 					<article class="markup mb-1">{@html comment.bodyHtml}</article>
 				{:else}
-					<article class="mb-1 whitespace-pre-wrap text-foreground-default">{comment.body}</article>
+					<article class="mb-1 whitespace-pre-wrap text-foreground-default">
+						{comment.body}
+					</article>
 				{/if}
-				<Reactions {reactions} subjectUri={comment.uri} onchange={(next) => (reactions = next)} />
+				<Reactions
+					{reactions}
+					subjectUri={comment.uri}
+					onchange={(next) => (reactions = next)}
+				/>
 			{/if}
 			{#if remove.error}
 				<ErrorAlert label={remove.error} />
diff --git a/web/src/lib/components/repo/pulls/PullCompose.stories.svelte b/web/src/lib/components/repo/pulls/PullCompose.stories.svelte
new file mode 100644
index 000000000..6234afc39
--- /dev/null
+++ b/web/src/lib/components/repo/pulls/PullCompose.stories.svelte
@@ -0,0 +1,109 @@
+<script module lang="ts">
+	import { defineMeta } from "@storybook/addon-svelte-csf";
+	import { expect, userEvent, within } from "storybook/test";
+	import PullCompose from "./PullCompose.svelte";
+	import MockAuthProvider, {
+		mockAccounts
+	} from "$lib/components/testing/MockAuthProvider.svelte";
+	import type { ComposeData } from "$lib/api/pullCompose";
+
+	const storyAccounts = mockAccounts.slice(0, 2);
+
+	const branch = (name: string, isDefault = false) => ({
+		reference: { name, hash: "d34db33fd34db33fd34db33fd34db33fd34db33f" },
+		is_default: isDefault,
+		commit: {
+			Committer: { Name: "alice", Email: "alice@example.com", When: "2026-08-10T12:00:00Z" }
+		}
+	});
+
+	const compose: ComposeData = {
+		commits: [
+			{
+				hash: "d34db33fd34db33fd34db33fd34db33fd34db33f",
+				shortHash: "d34db33",
+				subject: "compose: add account selector to the action row",
+				body: "",
+				authorName: "alice",
+				authorEmail: "alice@example.com",
+				when: "2026-08-12T12:00:00Z"
+			}
+		],
+		commitsError: "",
+		sourceRepoPath: "alice.pds.tngl.boltless.dev/core",
+		branches: [{ name: "main", hash: "abc123", isDefault: true }],
+		sourceBranches: [branch("feature/compose-selector")],
+		forkBranches: [branch("feature/compose-selector")],
+		forks: [
+			{
+				uri: "at://did:plc:alice/sh.tangled.repo/3m2k1",
+				repoDid: "did:plc:alice",
+				name: "core",
+				knot: "knot.example.test"
+			}
+		],
+		source: "fork",
+		sourceBranch: "feature/compose-selector",
+		targetBranch: "main",
+		fork: "did:plc:alice",
+		patch: "",
+		sourceRepoDid: "did:plc:alice",
+		sourceKnot: "knot.example.test",
+		showDetails: true,
+		prefillError: ""
+	};
+
+	const { Story } = defineMeta({
+		title: "Repo/Pulls/PullCompose",
+		component: PullCompose,
+		tags: ["autodocs"],
+		args: {
+			ownerHandle: "tangled.org",
+			repoName: "core",
+			repoDid: "did:plc:wshs7t2adsemcrrd4snkeqli",
+			repo: {
+				uri: "at://did:plc:wshs7t2adsemcrrd4snkeqli/sh.tangled.repo/3abc",
+				rkey: "3abc",
+				name: "core",
+				ownerDid: "did:plc:wshs7t2adsemcrrd4snkeqli",
+				ownerHandle: "tangled.org",
+				repoDid: "did:plc:wshs7t2adsemcrrd4snkeqli",
+				knot: "knot.example.test",
+				defaultBranch: "main"
+			},
+			bobbinUrl: "https://bobbin.example.test",
+			knotMirrorUrl: "https://mirror.example.test",
+			markup: { repo: "tangled.org/core", ref: "main", host: "tangled.org" },
+			compose
+		}
+	});
+</script>
+
+<Story name="Default">
+	{#snippet template(args)}
+		<MockAuthProvider accounts={storyAccounts}>
+			<PullCompose {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
+
+<Story
+	name="Multiaccount"
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		const trigger = canvas.getByRole("button", { name: /open as alice/i });
+		await expect(trigger).toBeInTheDocument();
+		await userEvent.click(trigger);
+		await userEvent.click(await canvas.findByRole("menuitem", { name: /bob/i }));
+		// the story's bobbin is fake, the diverged refetch fails and the fork
+		// lane falls back to its empty state
+		await canvas.findByText(/select a fork first/i, {}, { timeout: 5000 });
+		await expect(canvas.getByRole("button", { name: /open as bob/i })).toBeInTheDocument();
+	}}
+>
+	{#snippet template(args)}
+		<MockAuthProvider accounts={storyAccounts}>
+			<PullCompose {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
diff --git a/web/src/lib/components/repo/pulls/PullCompose.svelte b/web/src/lib/components/repo/pulls/PullCompose.svelte
index 02a5795db..63d8ad048 100644
--- a/web/src/lib/components/repo/pulls/PullCompose.svelte
+++ b/web/src/lib/components/repo/pulls/PullCompose.svelte
@@ -1,8 +1,10 @@
 <script lang="ts">
 	import { untrack } from "svelte";
+	import { SvelteURLSearchParams } from "svelte/reactivity";
 	import { goto } from "$app/navigation";
 	import { resolve } from "$app/paths";
 	import { now as tidNow } from "@atcute/tid";
+	import type { Did } from "@atcute/lexicons/syntax";
 	import ArrowLeftRight from "$icon/arrow-left-right";
 	import Copy from "$icon/copy";
 	import CopyCheck from "$icon/copy-check";
@@ -13,9 +15,15 @@
 	import { createBobbinClient } from "$lib/api/client";
 	import { getBranch, getMergeBase } from "$lib/api/knotmirror";
 	import { keepCommit, putPull } from "$lib/api/pull";
-	import { composeQuery, type PullSource } from "$lib/api/pullCompose";
+	import {
+		composeQuery,
+		loadCompose,
+		type ComposeData,
+		type PullSource
+	} from "$lib/api/pullCompose";
 	import { createAction } from "$lib/action.svelte";
 	import { getAuth } from "$lib/auth.svelte";
+	import AccountSelector from "$lib/components/auth/AccountSelector.svelte";
 	import Button from "$lib/components/ui/Button.svelte";
 	import ErrorAlert from "$lib/components/ui/Error.svelte";
 	import Field from "$lib/components/ui/Field.svelte";
@@ -26,67 +34,99 @@
 	import Textarea from "$lib/components/ui/Textarea.svelte";
 	import TimeAgo from "$lib/components/ui/TimeAgo.svelte";
 	import type { PullRecord } from "$lib/api/records";
-	import type { BranchEntry, BranchSummary, CommitSummary } from "$lib/api/repo";
+	import type { BranchEntry } from "$lib/api/repo";
 	import type { SelectOption } from "$lib/components/ui/selectField";
+	import type { RepoInfo } from "$lib/components/repo/types";
 	import type { MarkupContext } from "$lib/markup";
-	import type { ForkOption } from "../../../../routes/[handle]/[repo]/pulls/new/+page";
 	import { formatCount } from "$lib/format";
 
 	/** everything the route's load derived, passed through whole */
-	interface Compose {
-		branches: BranchSummary[];
-		sourceBranches: BranchEntry[];
-		forkBranches: BranchEntry[];
-		forks: ForkOption[];
-		source: PullSource;
-		sourceBranch: string;
-		targetBranch: string;
-		fork: string;
-		patch: string;
-		sourceRepoDid: string;
-		sourceKnot: string;
-		showDetails: boolean;
-		prefillError: string;
-		commits: CommitSummary[];
-		commitsError: string;
-		/** `owner/repo` of the source repo, for the browse-at-commit links */
-		sourceRepoPath: string;
-	}
-
 	interface Props {
 		ownerHandle: string;
 		repoName: string;
 		repoDid: string;
+		repo: RepoInfo;
+		bobbinUrl: string;
 		knotMirrorUrl: string;
 		markup: MarkupContext;
-		compose: Compose;
+		compose: ComposeData;
 	}
 
-	let { ownerHandle, repoName, repoDid, knotMirrorUrl, markup, compose }: Props = $props();
+	let { ownerHandle, repoName, repoDid, repo, bobbinUrl, knotMirrorUrl, markup, compose }: Props =
+		$props();
 
 	const auth = getAuth();
+	const accounts = $derived(auth?.accounts ?? []);
+
+	let picked = $state<string | null>(null);
+	const acting = $derived(
+		accounts.find((account) => account.did === (picked ?? auth?.currentDid))
+	);
+
+	// the load can't see the pick, a diverged one refetches the fork lane here
+	let diverged = $state<ComposeData | null>(null);
+	let laneLoading = $state(false);
+	$effect(() => {
+		if (!acting || acting.did === auth?.currentDid || compose.source !== "fork") {
+			diverged = null;
+			laneLoading = false;
+			return;
+		}
+		const params = new SvelteURLSearchParams(
+			composeQuery({
+				source: compose.source,
+				sourceBranch: compose.sourceBranch,
+				targetBranch: compose.targetBranch,
+				fork: compose.fork
+			})
+		);
+		if (compose.patch) params.set("patch", compose.patch);
+		let live = true;
+		laneLoading = true;
+		void loadCompose({
+			config: { bobbinUrl, knotMirrorUrl },
+			repo,
+			viewer: { did: acting.did, handle: acting.handle },
+			params,
+			fetch: globalThis.fetch
+		})
+			.then((lane) => {
+				if (!live) return;
+				diverged = lane;
+				laneLoading = false;
+			})
+			.catch(() => {
+				if (!live) return;
+				diverged = null;
+				laneLoading = false;
+			});
+		return () => {
+			live = false;
+		};
+	});
+	const view = $derived(diverged ?? compose);
 	const base = $derived(`/${ownerHandle}/${repoName}/pulls`);
 
 	let title = $state("");
 	let body = $state("");
 	// patch mode is not supported
-	let patch = $state(untrack(() => compose.patch));
+	let patch = $state(untrack(() => view.patch));
 
 	// selects rewrite the url and the load recomputes
 	const navigate = (
-		change: Partial<Pick<Compose, "source" | "sourceBranch" | "targetBranch" | "fork">>
+		change: Partial<Pick<ComposeData, "source" | "sourceBranch" | "targetBranch" | "fork">>
 	) => {
 		const next = {
-			source: compose.source,
-			sourceBranch: compose.sourceBranch,
-			targetBranch: compose.targetBranch,
-			fork: compose.fork,
+			source: view.source,
+			sourceBranch: view.sourceBranch,
+			targetBranch: view.targetBranch,
+			fork: view.fork,
 			...change
 		};
 		// a mode change drops the other mode's branch pick, which no longer names
 		// anything the new candidate list has
-		if (change.source && change.source !== compose.source) next.sourceBranch = "";
-		if (change.fork && change.fork !== compose.fork) next.sourceBranch = "";
+		if (change.source && change.source !== view.source) next.sourceBranch = "";
+		if (change.fork && change.fork !== view.fork) next.sourceBranch = "";
 		const query = composeQuery(next);
 		void goto(resolve(`${base}/new${query ? `?${query}` : ""}` as "/"), {
 			replaceState: true,
@@ -98,12 +138,12 @@
 	const defaultHint = (branch: BranchEntry) => (branch.is_default ? "default" : undefined);
 
 	const targetOptions = $derived(
-		compose.branches.map((branch): SelectOption => {
+		view.branches.map((branch): SelectOption => {
 			// picking the source as the target would compare a branch with itself
 			const isSource =
-				compose.source === "branch" &&
-				Boolean(compose.sourceBranch) &&
-				branch.name === compose.sourceBranch;
+				view.source === "branch" &&
+				Boolean(view.sourceBranch) &&
+				branch.name === view.sourceBranch;
 			return {
 				value: branch.name,
 				hint: isSource ? "source" : branch.isDefault ? "default" : undefined,
@@ -113,9 +153,9 @@
 	);
 
 	const branchOptions = $derived(
-		compose.sourceBranches.map((branch, index): SelectOption => {
+		view.sourceBranches.map((branch, index): SelectOption => {
 			const isTarget =
-				Boolean(compose.targetBranch) && branch.reference.name === compose.targetBranch;
+				Boolean(view.targetBranch) && branch.reference.name === view.targetBranch;
 			return {
 				value: branch.reference.name,
 				// the list is recency sorted, so the head of it is the newest branch
@@ -126,7 +166,7 @@
 	);
 
 	const forkBranchOptions = $derived(
-		compose.forkBranches.map((branch, index): SelectOption => ({
+		view.forkBranches.map((branch, index): SelectOption => ({
 			value: branch.reference.name,
 			hint: index === 0 ? "new" : defaultHint(branch)
 		}))
@@ -140,7 +180,7 @@
 	};
 
 	const forkOptions = $derived(
-		compose.forks.map((fork): SelectOption => ({
+		view.forks.map((fork): SelectOption => ({
 			value: fork.repoDid,
 			label: `${ownerHandle}/${fork.name}`
 		}))
@@ -148,20 +188,21 @@
 
 	const save = createAction(async (event: SubmitEvent) => {
 		event.preventDefault();
-		const agent = auth.agent;
-		if (!agent) throw new Error("You must be signed in to open a pull request.");
+		if (!auth || !acting) throw new Error("You must be signed in to open a pull request.");
 
 		if (title.trim() === "") throw new Error("Title is required");
-		if (!compose.targetBranch) throw new Error("Target branch is required.");
-		if (compose.source === "patch") throw new Error("Patch based PR is currently unsupported.");
-		if (!compose.sourceBranch) throw new Error("Neither source branch nor patch supplied.");
-		if (compose.sourceRepoDid === repoDid && compose.sourceBranch === compose.targetBranch) {
+		if (!view.targetBranch) throw new Error("Target branch is required.");
+		if (view.source === "patch") throw new Error("Patch based PR is currently unsupported.");
+		if (!view.sourceBranch) throw new Error("Neither source branch nor patch supplied.");
+		if (view.sourceRepoDid === repoDid && view.sourceBranch === view.targetBranch) {
 			throw new Error("Source and target branch must be different.");
 		}
 		if (!knotMirrorUrl) {
 			throw new Error("No knot mirror is configured, so branch refs can't be resolved.");
 		}
 
+		const agent = await auth.agentFor(acting.did as Did);
+
 		// keepCommit pins against the record's at-uri, so the rkey is minted first
 		const rkey = tidNow();
 		const uri = `at://${agent.sub}/sh.tangled.repo.pull/${rkey}`;
@@ -169,21 +210,21 @@
 
 		const [mergeBase, head] = await Promise.all([
 			getMergeBase(mirror, {
-				repo: compose.sourceRepoDid,
-				base: compose.targetBranch,
-				head: compose.sourceBranch
+				repo: view.sourceRepoDid,
+				base: view.targetBranch,
+				head: view.sourceBranch
 			}),
-			getBranch(mirror, { repo: compose.sourceRepoDid, name: compose.sourceBranch })
+			getBranch(mirror, { repo: view.sourceRepoDid, name: view.sourceBranch })
 		]);
 
 		// pin before the record lands, so gc can't drop the head in between
 		console.log("keepCommit", {
-			repo: compose.sourceRepoDid,
+			repo: view.sourceRepoDid,
 			oid: head.hash,
 			record: uri
 		});
-		await keepCommit(agent, compose.sourceKnot, {
-			repo: compose.sourceRepoDid,
+		await keepCommit(agent, view.sourceKnot, {
+			repo: view.sourceRepoDid,
 			oid: head.hash,
 			record: uri
 		});
@@ -193,10 +234,10 @@
 			$type: "sh.tangled.repo.pull",
 			title,
 			body,
-			target: { repo: repoDid, branch: compose.targetBranch } as PullRecord["target"],
+			target: { repo: repoDid, branch: view.targetBranch } as PullRecord["target"],
 			source: {
-				repo: compose.sourceRepoDid,
-				branch: compose.sourceBranch
+				repo: view.sourceRepoDid,
+				branch: view.sourceBranch
 			} as PullRecord["source"],
 			rounds: [],
 			versions: [{ base: mergeBase.commit, head: head.hash, createdAt }],
@@ -252,8 +293,8 @@
 	<button
 		type="button"
 		{disabled}
-		class="{tabBase} {compose.source === mode ? tabActive : tabIdle}"
-		onclick={() => compose.source !== mode && navigate({ source: mode })}
+		class="{tabBase} {view.source === mode ? tabActive : tabIdle}"
+		onclick={() => view.source !== mode && navigate({ source: mode })}
 	>
 		<span class="typography-paragraph-small font-medium text-foreground-default">{heading}</span
 		>
@@ -262,12 +303,12 @@
 {/snippet}
 
 <div class="flex flex-col">
-	{#if compose.prefillError}
+	{#if view.prefillError}
 		<div
 			class="mb-4 flex items-center gap-2 rounded-sm border border-border-danger bg-background-danger-subtle px-3 py-2 typography-paragraph-small text-foreground-danger"
 		>
 			<TriangleAlert class="size-4 shrink-0" aria-hidden="true" />
-			<span>{compose.prefillError}</span>
+			<span>{view.prefillError}</span>
 		</div>
 	{/if}
 
@@ -281,6 +322,14 @@
 				>
 					Source
 				</h3>
+				<AccountSelector
+					{accounts}
+					bind:value={() => acting?.did ?? "", (did) => (picked = did)}
+					label="Open as"
+					disabled={save.loading}
+					group="pull-compose"
+					class="ml-auto"
+				/>
 			</div>
 			<div class="ml-10 flex flex-col gap-3">
 				<div
@@ -296,7 +345,7 @@
 					)}
 				</div>
 
-				{#if compose.source === "patch"}
+				{#if view.source === "patch"}
 					<Field label="Merge into" class="max-w-xs">
 						{#snippet children({ id })}
 							<Select
@@ -304,8 +353,8 @@
 								{...branchSearch}
 								label="Merge into"
 								options={targetOptions}
-								value={compose.targetBranch}
-								placeholder={compose.targetBranch ? undefined : "Target branch"}
+								value={view.targetBranch}
+								placeholder={view.targetBranch ? undefined : "Target branch"}
 								onSelect={(value) => navigate({ targetBranch: value })}
 							/>
 						{/snippet}
@@ -331,26 +380,27 @@
 									{...branchSearch}
 									label="Merge into"
 									options={targetOptions}
-									value={compose.targetBranch}
-									placeholder={compose.targetBranch ? undefined : "Target branch"}
+									value={view.targetBranch}
+									placeholder={view.targetBranch ? undefined : "Target branch"}
 									onSelect={(value) => navigate({ targetBranch: value })}
 								/>
 							{/snippet}
 						</Field>
 
-						{#if compose.source === "fork"}
+						{#if view.source === "fork"}
 							<Field label="Pull from" class="min-w-48">
 								{#snippet children({ id })}
 									<Select
 										{id}
 										options={forkOptions}
-										value={compose.fork}
-										placeholder={compose.fork ? undefined : "Select a fork"}
+										value={view.fork}
+										placeholder={view.fork ? undefined : "Select a fork"}
+										disabled={laneLoading}
 										onSelect={(value) => navigate({ fork: value })}
 									/>
 								{/snippet}
 							</Field>
-							{#if compose.fork && compose.forkBranches.length > 0}
+							{#if view.fork && view.forkBranches.length > 0}
 								<Field label="Branch" class="min-w-48">
 									{#snippet children({ id })}
 										<Select
@@ -358,8 +408,8 @@
 											{...branchSearch}
 											label="Branch"
 											options={forkBranchOptions}
-											value={compose.sourceBranch}
-											placeholder={compose.sourceBranch
+											value={view.sourceBranch}
+											placeholder={view.sourceBranch
 												? undefined
 												: "Source branch"}
 											onSelect={(value) => navigate({ sourceBranch: value })}
@@ -381,8 +431,8 @@
 										{...branchSearch}
 										label="Pull from"
 										options={branchOptions}
-										value={compose.sourceBranch}
-										placeholder={compose.sourceBranch
+										value={view.sourceBranch}
+										placeholder={view.sourceBranch
 											? undefined
 											: "Source branch"}
 										onSelect={(value) => navigate({ sourceBranch: value })}
@@ -406,19 +456,19 @@
 				</h3>
 			</div>
 			<div class="ml-10 flex flex-col gap-3">
-				{#if !compose.showDetails}
+				{#if !view.showDetails}
 					{@render notice(
-						compose.source === "patch"
+						view.source === "patch"
 							? "Paste a patch above to see a comparison."
 							: "Pick a source and target above to see a comparison."
 					)}
-				{:else if compose.source === "patch"}
+				{:else if view.source === "patch"}
 					<!-- TODO: implement patch based PR -->
-				{:else if compose.commitsError}
-					{@render notice(compose.commitsError, true)}
-				{:else if compose.commits.length === 0}
+				{:else if view.commitsError}
+					{@render notice(view.commitsError, true)}
+				{:else if view.commits.length === 0}
 					{@render notice(
-						compose.sourceBranch === compose.targetBranch
+						view.sourceBranch === view.targetBranch
 							? "Source and target are the same branch, nothing to merge."
 							: "No commits between target and source. Make sure your source branch has commits not on the target."
 					)}
@@ -427,19 +477,19 @@
 						class="flex min-w-0 items-center justify-between gap-3 typography-paragraph-small text-foreground-muted"
 					>
 						<span class="shrink-0">
-							{formatCount(compose.commits.length)}
-							{compose.commits.length === 1 ? "commit" : "commits"}
+							{formatCount(view.commits.length)}
+							{view.commits.length === 1 ? "commit" : "commits"}
 						</span>
 						<span
 							class="inline-flex items-center gap-2 truncate typography-monospace-small text-foreground-subtle"
 						>
-							<span>{compose.targetBranch}</span>
+							<span>{view.targetBranch}</span>
 							<ArrowLeftRight class="size-4 shrink-0" aria-hidden="true" />
-							<span>{compose.sourceBranch}</span>
+							<span>{view.sourceBranch}</span>
 						</span>
 					</div>
 					<ul class="m-0 flex list-none flex-col gap-2 p-0">
-						{#each compose.commits as commit (commit.hash)}
+						{#each view.commits as commit (commit.hash)}
 							<li
 								class="flex items-center gap-3 rounded-sm border border-border-default bg-background-default px-3 py-2"
 							>
@@ -476,7 +526,7 @@
 									</button>
 									<a
 										href={resolve(
-											`/${compose.sourceRepoPath}/tree/${commit.hash}` as "/"
+											`/${view.sourceRepoPath}/tree/${commit.hash}` as "/"
 										)}
 										class="rounded-sm p-1 text-foreground-subtle hover:bg-background-muted"
 										title="Browse repository at this commit"
@@ -496,7 +546,7 @@
 			</div>
 		</section>
 
-		{#if compose.showDetails}
+		{#if view.showDetails}
 			<section class="relative flex flex-col gap-3">
 				<div
 					class="{connector} -top-6 -bottom-12 mask-[linear-gradient(to_bottom,black_calc(100%-1.5rem),transparent)]"
diff --git a/web/src/lib/components/shell/Topbar.stories.svelte b/web/src/lib/components/shell/Topbar.stories.svelte
new file mode 100644
index 000000000..ba326cbac
--- /dev/null
+++ b/web/src/lib/components/shell/Topbar.stories.svelte
@@ -0,0 +1,35 @@
+<script module lang="ts">
+	import { defineMeta } from "@storybook/addon-svelte-csf";
+	import { expect, fn, userEvent, waitFor, within } from "storybook/test";
+	import type { Did } from "@atcute/lexicons/syntax";
+	import type { AuthAccount } from "$lib/auth.svelte";
+	import Topbar from "./Topbar.svelte";
+
+	const user = { did: "did:plc:alice" as Did, handle: "alice.tangled.sh" };
+	const accounts: AuthAccount[] = [
+		{ did: user.did, handle: user.handle, addedAt: 1 },
+		{ did: "did:plc:bob" as Did, handle: "bob.tangled.sh", addedAt: 2 }
+	];
+
+	const { Story } = defineMeta({
+		title: "Shell/Topbar",
+		component: Topbar,
+		tags: ["autodocs"],
+		args: { variant: "app", user }
+	});
+</script>
+
+<Story name="One account" args={{ accounts: [accounts[0]] }} />
+
+<Story name="Signed out" args={{ variant: "marketing", user: null }} />
+
+<Story
+	name="Switching account"
+	args={{ accounts, onSwitchAccount: fn() }}
+	play={async ({ canvasElement, args }) => {
+		const canvas = within(canvasElement);
+		await userEvent.click(canvas.getByRole("button", { name: /alice/i }));
+		await userEvent.click(await canvas.findByRole("menuitem", { name: /bob/i }));
+		await waitFor(() => expect(args.onSwitchAccount).toHaveBeenCalledWith("did:plc:bob"));
+	}}
+/>
diff --git a/web/src/lib/components/shell/Topbar.svelte b/web/src/lib/components/shell/Topbar.svelte
index 08e18b1b2..adb93bba1 100644
--- a/web/src/lib/components/shell/Topbar.svelte
+++ b/web/src/lib/components/shell/Topbar.svelte
@@ -15,7 +15,10 @@
 			link: "flex items-center text-foreground-default transition-colors hover:text-foreground-muted",
 			identity: "flex items-center",
 			ball: "size-8 rounded-full bg-background-inset md:size-5",
-			bar: "hidden h-4 w-24 rounded-sm bg-background-inset md:block"
+			bar: "hidden h-4 w-24 rounded-sm bg-background-inset md:block",
+			switchHeader: "px-2 py-1.5 typography-paragraph-small text-foreground-muted",
+			addBall:
+				"flex size-4.25 shrink-0 items-center justify-center rounded-full border border-border-default bg-background-canvas"
 		},
 		variants: {
 			variant: {
@@ -61,20 +64,33 @@
 	import Logo from "../ui/Logo.svelte";
 	import User from "../ui/User.svelte";
 	import TopbarSearch from "./TopbarSearch.svelte";
-	import type { CurrentUser } from "$lib/auth.svelte";
+	import type { AuthAccount, CurrentUser } from "$lib/auth.svelte";
 	import Separator from "../ui/Separator.svelte";
 
 	interface Props {
 		variant: NonNullable<TopbarVariants["variant"]>;
 		onSignOut?: () => void | Promise<void>;
+		onSwitchAccount?: (did: AuthAccount["did"]) => void | Promise<void>;
 		user: CurrentUser | null;
+		accounts?: readonly AuthAccount[];
+		addAccountHref?: string;
 		loading?: boolean;
 	}
 
-	let { variant, onSignOut, user, loading = false }: Props = $props();
+	let {
+		variant,
+		onSignOut,
+		onSwitchAccount,
+		user,
+		accounts = [],
+		addAccountHref = "/login",
+		loading = false
+	}: Props = $props();
 
 	const appPath = (path: string) => resolve(path as "/");
 
+	const others = $derived(accounts.filter((account) => account.did !== user?.did));
+
 	const style = $derived(topbar({ variant }));
 </script>
 
@@ -124,8 +140,12 @@
 								<Plus class="size-3.5" aria-hidden="true" />
 								<span class="hidden md:inline">New</span>
 							{/snippet}
-							<DropdownItem href="/repo/new" icon={BookPlus}>New repository</DropdownItem>
-							<DropdownItem href="/strings/new" icon={LineSquiggle}>New string</DropdownItem>
+							<DropdownItem href="/repo/new" icon={BookPlus}
+								>New repository</DropdownItem
+							>
+							<DropdownItem href="/strings/new" icon={LineSquiggle}
+								>New string</DropdownItem
+							>
 						</Dropdown>
 					</div>
 
@@ -156,7 +176,11 @@
 
 				<div class={style.action({ class: "order-4 md:order-5" })}>
 					{#if loading}
-						<div class={style.identity({ pending: true })} role="status" aria-label="Signing in">
+						<div
+							class={style.identity({ pending: true })}
+							role="status"
+							aria-label="Signing in"
+						>
 							<span class={style.ball({ pending: true })}>
 								<Spinner class="size-4" />
 							</span>
@@ -174,7 +198,28 @@
 							{#snippet trigger()}
 								<User did={user.did} handle={user.handle} />
 							{/snippet}
-							<DropdownItem href={`/${user.handle}`} icon={UserIcon}>Profile</DropdownItem>
+							{#if others.length > 0}
+								<div class={style.switchHeader()}>Switch account</div>
+								{#each others as account (account.did)}
+									<DropdownItem onclick={() => onSwitchAccount?.(account.did)}>
+										<User
+											did={account.did}
+											handle={account.handle}
+											size="small"
+										/>
+									</DropdownItem>
+								{/each}
+							{/if}
+							<DropdownItem href={addAccountHref}>
+								<span class={style.addBall()}>
+									<Plus class="size-2.5" aria-hidden="true" />
+								</span>
+								Add account
+							</DropdownItem>
+							<Separator />
+							<DropdownItem href={`/${user.handle}`} icon={UserIcon}
+								>Profile</DropdownItem
+							>
 							<DropdownItem href={`/${user.handle}?tab=repos`} icon={BookMarked}>
 								Repositories
 							</DropdownItem>
@@ -182,8 +227,9 @@
 								Strings
 							</DropdownItem>
 							<DropdownItem href="/settings" icon={Cog}>Settings</DropdownItem>
-							<Separator />
-							<DropdownItem danger icon={LogOut} onclick={onSignOut}>Logout</DropdownItem>
+							<DropdownItem danger icon={LogOut} onclick={onSignOut}
+								>Logout</DropdownItem
+							>
 						</Dropdown>
 					{:else}
 						<div class={style.identity()} aria-hidden="true">
diff --git a/web/src/lib/components/strings/StringForm.stories.svelte b/web/src/lib/components/strings/StringForm.stories.svelte
new file mode 100644
index 000000000..35d9958e5
--- /dev/null
+++ b/web/src/lib/components/strings/StringForm.stories.svelte
@@ -0,0 +1,62 @@
+<script module lang="ts">
+	import { defineMeta } from "@storybook/addon-svelte-csf";
+	import { expect, userEvent, waitFor, within } from "storybook/test";
+	import MockAuthProvider, {
+		mockAccounts
+	} from "$lib/components/testing/MockAuthProvider.svelte";
+	import StringForm from "./StringForm.svelte";
+
+	const noop = () => undefined;
+
+	const storyAccounts = mockAccounts.slice(0, 2);
+
+	const { Story } = defineMeta({
+		title: "Strings/StringForm",
+		component: StringForm,
+		tags: ["autodocs"],
+		args: {
+			mode: "create",
+			filename: "hello.rs",
+			description: "a tiny snippet",
+			content: 'fn main() {\n\tprintln!("hello");\n}',
+			onsaved: noop,
+			oncancel: noop
+		}
+	});
+</script>
+
+<Story name="Create" />
+
+<Story
+	name="Publishing as another account"
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		await userEvent.click(canvas.getByRole("button", { name: /publish as alice/i }));
+		await userEvent.click(await canvas.findByRole("menuitem", { name: /bob/i }));
+		await waitFor(() =>
+			expect(canvas.getByRole("button", { name: /publish as bob/i })).toBeVisible()
+		);
+	}}
+>
+	{#snippet template(args)}
+		<MockAuthProvider accounts={storyAccounts}>
+			<StringForm {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
+
+<Story
+	name="Editing has no picker"
+	args={{ mode: "edit", rkey: "3l7abc" }}
+	play={async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		expect(canvas.queryByRole("button", { name: /publish as/i })).toBeNull();
+		await waitFor(() => expect(canvas.getByRole("button", { name: "Publish" })).toBeVisible());
+	}}
+>
+	{#snippet template(args)}
+		<MockAuthProvider accounts={storyAccounts}>
+			<StringForm {...args} />
+		</MockAuthProvider>
+	{/snippet}
+</Story>
diff --git a/web/src/lib/components/strings/StringForm.svelte b/web/src/lib/components/strings/StringForm.svelte
index e5be2792c..57fa6083f 100644
--- a/web/src/lib/components/strings/StringForm.svelte
+++ b/web/src/lib/components/strings/StringForm.svelte
@@ -1,5 +1,6 @@
 <script lang="ts">
 	import { untrack } from "svelte";
+	import type { Did } from "@atcute/lexicons/syntax";
 	import { now as tidNow } from "@atcute/tid";
 	import Button from "$lib/components/ui/Button.svelte";
 	import Spinner from "$lib/components/ui/Spinner.svelte";
@@ -7,6 +8,7 @@
 	import ArrowUp from "$icon/arrow-up";
 	import X from "$icon/x";
 	import { getAuth } from "$lib/auth.svelte";
+	import AccountSelector from "$lib/components/auth/AccountSelector.svelte";
 	import { putString } from "$lib/api/strings";
 	import type { StringRecord } from "$lib/api/records";
 	import { createAction } from "$lib/action.svelte";
@@ -18,7 +20,7 @@
 		filename?: string;
 		description?: string;
 		content?: string;
-		onsaved: (rkey: string) => void;
+		onsaved: (rkey: string, handle: string) => void;
 		oncancel?: () => void;
 	}
 
@@ -34,6 +36,15 @@
 	}: Props = $props();
 
 	const auth = getAuth();
+	const accounts = $derived(auth?.accounts ?? []);
+
+	let picked = $state<string | null>(null);
+	const acting = $derived(
+		accounts.find((account) => account.did === picked) ?? {
+			did: auth?.currentDid ?? "",
+			handle: auth?.currentUser?.handle ?? ""
+		}
+	);
 
 	let filename = $state(untrack(() => initialFilename));
 	let description = $state(untrack(() => initialDescription));
@@ -44,8 +55,8 @@
 
 	const publish = createAction(async (event: SubmitEvent) => {
 		event.preventDefault();
-		const agent = auth.agent;
-		if (!agent) return;
+		if (!auth?.currentDid) return;
+		const agent = await auth.agentFor(acting.did as Did);
 		const targetRkey = rkey ?? tidNow();
 		const record: StringRecord = {
 			$type: "sh.tangled.string",
@@ -55,7 +66,7 @@
 			createdAt: createdAt ?? new Date().toISOString()
 		};
 		await putString(agent, targetRkey, record);
-		onsaved(targetRkey);
+		onsaved(targetRkey, acting.handle);
 	});
 </script>
 
@@ -117,6 +128,15 @@
 						Cancel
 					</Button>
 				{/if}
+				{#if mode === "create"}
+					<AccountSelector
+						{accounts}
+						bind:value={() => acting.did, (did) => (picked = did)}
+						label="Publish as"
+						disabled={publish.loading}
+						group="string-form"
+					/>
+				{/if}
 				<Button
 					type="submit"
 					variant="primary"
diff --git a/web/src/lib/components/testing/MockAuthProvider.svelte b/web/src/lib/components/testing/MockAuthProvider.svelte
index 4eeccd266..f762ecfdc 100644
--- a/web/src/lib/components/testing/MockAuthProvider.svelte
+++ b/web/src/lib/components/testing/MockAuthProvider.svelte
@@ -1,3 +1,11 @@
+<script module lang="ts">
+	export const mockAccounts = [
+		{ did: "did:plc:alice", handle: "alice.pds.tngl.boltless.dev" },
+		{ did: "did:plc:bob", handle: "bob.pds.tngl.boltless.dev" },
+		{ did: "did:plc:carol", handle: "carol.pds.tngl.boltless.dev" }
+	];
+</script>
+
 <script lang="ts">
 	// story-only helper: injects a fake auth context so form stories can exercise
 	// a real (failing) submission without a live session. the fake agent's fetch
@@ -11,12 +19,17 @@
 		// when false, injects a signed-out context (no agent / null did) so stories
 		// can exercise the logged-out affordance
 		signedIn?: boolean;
+		accounts?: { did: string; handle: string }[];
+		// dids whose session is expired
+		expired?: string[];
 		children: Snippet;
 	}
 
 	let {
 		failWith = "MockAuthProvider: network request failed, this error is intentional.",
 		signedIn = true,
+		accounts = [mockAccounts[0]],
+		expired = [],
 		children
 	}: Props = $props();
 
@@ -29,15 +42,37 @@
 			}
 		: null;
 
+	// svelte-ignore state_referenced_locally
+	let knownAccounts = $state(accounts.map((account, index) => ({ ...account, addedAt: index })));
+
 	// svelte-ignore state_referenced_locally
 	const auth = (signedIn
 		? {
 				agent,
-				currentDid: "did:plc:alice",
-				currentUser: { did: "did:plc:alice", handle: "alice.pds.tngl.boltless.dev" },
+				currentDid: knownAccounts[0]?.did ?? null,
+				currentUser: knownAccounts[0] ?? null,
+				get accounts() {
+					return knownAccounts;
+				},
+				hasAccount: (did: string) => knownAccounts.some((account) => account.did === did),
+				agentFor: (did: string) => {
+					if (!expired.includes(did)) return Promise.resolve(agent);
+					const handle =
+						knownAccounts.find((account) => account.did === did)?.handle ?? did;
+					knownAccounts = knownAccounts.filter((account) => account.did !== did);
+					return Promise.reject(
+						new Error(`${handle}'s session expired. Sign in again to act as them.`)
+					);
+				},
 				bobbinUrl: "https://bobbin.story"
 			}
-		: { agent: null, currentDid: null, currentUser: null }) as unknown as Auth;
+		: {
+				agent: null,
+				currentDid: null,
+				currentUser: null,
+				accounts: [],
+				hasAccount: () => false
+			}) as unknown as Auth;
 
 	setContext(AUTH_KEY, auth);
 </script>
diff --git a/web/src/lib/components/ui/Dropdown.svelte b/web/src/lib/components/ui/Dropdown.svelte
index 95882b615..ee26af122 100644
--- a/web/src/lib/components/ui/Dropdown.svelte
+++ b/web/src/lib/components/ui/Dropdown.svelte
@@ -5,7 +5,8 @@
 	export const dropdown = tv({
 		slots: {
 			root: "relative inline-flex",
-			plainTrigger: "min-h-0 gap-1 border-0 bg-transparent p-0 text-inherit hover:bg-transparent",
+			plainTrigger:
+				"min-h-0 gap-1 border-0 bg-transparent p-0 text-inherit hover:bg-transparent",
 			menu: "dropdown-menu fixed z-50 m-0 max-h-[calc(100dvh-1rem)] w-56 max-w-[calc(100vw-1rem)] popover-transition divide-y divide-border-default overflow-auto rounded-sm border border-border-default bg-background-default text-foreground-default shadow-regular"
 		},
 		variants: {
@@ -60,7 +61,9 @@
 		insetShadow?: ButtonVariants["insetShadow"];
 		align?: DropdownVariants["align"];
 		label?: string;
+		disabled?: boolean;
 		menuClass?: string;
+		class?: string;
 		trigger: Snippet;
 		children: Snippet;
 		xOffset?: number;
@@ -75,7 +78,9 @@
 		size,
 		align = "left",
 		label,
+		disabled = false,
 		menuClass,
+		class: className,
 		trigger,
 		children,
 		xOffset
@@ -179,11 +184,11 @@
 	});
 </script>
 
-<div class={classes.root()}>
+<div class={classes.root({ class: className })}>
 	<Button
 		bind:ref={triggerElement}
 		variant={variant === "button" ? buttonVariant : "ghost"}
-		size={size}
+		{size}
 		class={variant === "button" ? undefined : classes.plainTrigger()}
 		popovertarget={menuId}
 		popovertargetaction="toggle"
@@ -193,6 +198,7 @@
 		aria-controls={menuId}
 		aria-label={label}
 		{insetShadow}
+		{disabled}
 	>
 		{@render trigger()}
 	</Button>
diff --git a/web/src/routes/+layout.svelte b/web/src/routes/+layout.svelte
index f37185b9e..40e622cb1 100644
--- a/web/src/routes/+layout.svelte
+++ b/web/src/routes/+layout.svelte
@@ -1,6 +1,9 @@
 <script lang="ts">
 	import { dev } from "$app/environment";
 	import { page } from "$app/state";
+	import { goto, invalidateAll } from "$app/navigation";
+	import { resolve } from "$app/paths";
+	import type { Did } from "@atcute/lexicons/syntax";
 	import { createAuth, AUTH_KEY } from "$lib/auth.svelte";
 	import Agentation from "$lib/components/dev/Agentation.svelte";
 	import Footer from "$lib/components/shell/Footer.svelte";
@@ -20,6 +23,26 @@
 		if (page.url.pathname !== "/oauth/callback") void auth.refresh();
 	});
 
+	const switchAccount = async (did: Did) => {
+		const returnTo = page.url.pathname + page.url.search;
+		const handle = auth.accounts.find((account) => account.did === did)?.handle ?? did;
+		try {
+			if (await auth.switchAccount(did, returnTo)) await invalidateAll();
+		} catch {
+			const query = new URLSearchParams({
+				error: "session",
+				identifier: handle,
+				return_url: returnTo
+			});
+			await goto(resolve(`/login?${query}` as "/login"));
+		}
+	};
+
+	const signOut = async () => {
+		await auth.signOut();
+		await invalidateAll();
+	};
+
 	const signedIn = $derived(Boolean(auth.currentUser));
 	const isAuthShell = $derived(page.url.pathname === "/login");
 	// the welcome flow runs its own steps chrome, so the bar and footer step aside
@@ -49,9 +72,13 @@
 		>
 			<Topbar
 				user={auth.currentUser}
+				accounts={auth.accounts}
+				addAccountHref={`/login?return_url=${encodeURIComponent(page.url.pathname)}`}
 				variant={topbarVariant}
-				loading={auth.state.kind === "authenticating" || auth.state.kind === "profile-loading"}
-				onSignOut={auth.signOut}
+				loading={auth.state.kind === "authenticating" ||
+					auth.state.kind === "profile-loading"}
+				onSignOut={signOut}
+				onSwitchAccount={switchAccount}
 			/>
 		</header>
 	{/if}
diff --git a/web/src/routes/[handle]/[repo]/issues/[aturi]/+page.svelte b/web/src/routes/[handle]/[repo]/issues/[aturi]/+page.svelte
index 5b2d72226..5fd364b5a 100644
--- a/web/src/routes/[handle]/[repo]/issues/[aturi]/+page.svelte
+++ b/web/src/routes/[handle]/[repo]/issues/[aturi]/+page.svelte
@@ -18,6 +18,7 @@
 	import { deleteIssue, type IssueRecord } from "$lib/api/issue";
 	import type { RecordView } from "$lib/api/records";
 	import type { ThreadInput } from "$lib/components/comment/comments";
+	import type { Did } from "@atcute/lexicons/syntax";
 	import { getAuth } from "$lib/auth.svelte";
 	import { createAction } from "$lib/action.svelte";
 
@@ -27,7 +28,7 @@
 
 	let issue = $derived(data.issue);
 
-	const isAuthor = $derived(auth.currentUser?.did === issue.authorDid);
+	const isAuthor = $derived(auth.hasAccount(issue.authorDid));
 	const issuesBase = $derived(`/${data.repo.ownerHandle}/${data.repo.name}/issues`);
 
 	let editing = $state(false);
@@ -40,7 +41,9 @@
 			comments = [...comments, { self: comment, replies: [] }];
 		} else {
 			comments = comments.map((thread) =>
-				thread.self.uri === replyTo ? { ...thread, replies: [...thread.replies, comment] } : thread
+				thread.self.uri === replyTo
+					? { ...thread, replies: [...thread.replies, comment] }
+					: thread
 			);
 		}
 	};
@@ -59,7 +62,10 @@
 				// replies remain grouped; otherwise drop it entirely
 				if (thread.self.uri === uri) {
 					return thread.replies.length
-						? { ...thread, self: { ...thread.self, body: "", bodyHtml: null, deleted: true } }
+						? {
+								...thread,
+								self: { ...thread.self, body: "", bodyHtml: null, deleted: true }
+							}
 						: null;
 				}
 				return { ...thread, replies: thread.replies.filter((reply) => reply.uri !== uri) };
@@ -75,14 +81,13 @@
 	};
 
 	const removeIssue = createAction(async () => {
-		const agent = auth.agent;
-		if (!agent) return;
+		const agent = await auth.agentFor(issue.authorDid as Did);
 		await deleteIssue(agent, issue.rkey);
 		await goto(resolve(issuesBase as "/"));
 	});
 
 	const handleDelete = () => {
-		if (!auth.agent || removeIssue.loading) return;
+		if (!auth.currentDid || removeIssue.loading) return;
 		if (!confirm("Delete this issue? This cannot be undone.")) return;
 		void removeIssue.run();
 	};
@@ -90,7 +95,8 @@
 
 <svelte:head>
 	<title
-		>{issue.title} &middot; Issue #{issue.rkey} &middot; {data.repo.ownerHandle}/{data.repo.name}
+		>{issue.title} &middot; Issue #{issue.rkey} &middot; {data.repo.ownerHandle}/{data.repo
+			.name}
 		&middot; Tangled</title
 	>
 </svelte:head>
@@ -122,6 +128,7 @@
 			{#if editing}
 				<IssueForm
 					mode="edit"
+					authorDid={issue.authorDid}
 					repoDid={data.repo.repoDid ?? ""}
 					markup={data.markup}
 					rkey={issue.rkey}
@@ -141,7 +148,12 @@
 					actions={isAuthor ? issueActions : undefined}
 				/>
 				<IssueBody body={issue.body} bodyHtml={issue.bodyHtml} />
-				<Reactions reactions={issue.reactions} subjectUri={issue.uri} alwaysShow class="mt-2" />
+				<Reactions
+					reactions={issue.reactions}
+					subjectUri={issue.uri}
+					alwaysShow
+					class="mt-2"
+				/>
 				{#if removeIssue.error}
 					<div class="mt-3">
 						<ErrorAlert label={removeIssue.error} />
diff --git a/web/src/routes/[handle]/[repo]/pulls/new/+page.svelte b/web/src/routes/[handle]/[repo]/pulls/new/+page.svelte
index f8892b497..3c9252581 100644
--- a/web/src/routes/[handle]/[repo]/pulls/new/+page.svelte
+++ b/web/src/routes/[handle]/[repo]/pulls/new/+page.svelte
@@ -23,6 +23,8 @@
 		ownerHandle={data.repo.ownerHandle}
 		repoName={data.repo.name}
 		repoDid={data.repo.repoDid ?? ""}
+		repo={data.repo}
+		bobbinUrl={data.publicConfig.bobbinUrl}
 		knotMirrorUrl={data.publicConfig.knotMirrorUrl}
 		compose={data}
 	/>
diff --git a/web/src/routes/[handle]/[repo]/pulls/new/+page.ts b/web/src/routes/[handle]/[repo]/pulls/new/+page.ts
index 05eb9dd26..ce7880efe 100644
--- a/web/src/routes/[handle]/[repo]/pulls/new/+page.ts
+++ b/web/src/routes/[handle]/[repo]/pulls/new/+page.ts
@@ -1,137 +1,16 @@
 import { error } from "@sveltejs/kit";
-import { createBobbinClient } from "$lib/api/client";
-import { branches as listBranches, gitTarget } from "$lib/api/gitclient";
-import { listCommits, toMirrorCommitSummary } from "$lib/api/gitmirror";
-import {
-	defaultSourceBranch,
-	defaultTargetBranch,
-	parseSource,
-	sortBranchesByRecency,
-	sourceBranchChoices,
-	type PullSource
-} from "$lib/api/pullCompose";
-import { listRepos } from "$lib/api/records";
-import { repoNameOf, sortBranches, toBranchSummary } from "$lib/api/repo";
-import type { Did } from "@atcute/lexicons/syntax";
-import type { BranchEntry, CommitSummary } from "$lib/api/repo";
+import { loadCompose } from "$lib/api/pullCompose";
 import type { PageLoad } from "./$types";
 
-const BRANCH_LIMIT = 500;
-const COMMIT_LIMIT = 100;
-
-/** one of the viewer's forks, as the fork picker needs it */
-export interface ForkOption {
-	uri: string;
-	repoDid: string;
-	name: string;
-	knot: string;
-}
-
 export const load: PageLoad = async (event) => {
 	const parent = await event.parent();
-	const repoDid = parent.repo.repoDid;
-	if (!repoDid) error(404, "This repository has not been indexed yet");
+	if (!parent.repo.repoDid) error(404, "This repository has not been indexed yet");
 
-	const ctx = createBobbinClient({
-		serviceUrl: parent.publicConfig.bobbinUrl,
+	return loadCompose({
+		config: parent.publicConfig,
+		repo: parent.repo,
+		viewer: parent.auth,
+		params: event.url.searchParams,
 		fetch: event.fetch
 	});
-	const params = event.url.searchParams;
-	const source: PullSource = parseSource(params.get("source")) ?? "branch";
-	const viewerDid = parent.auth?.did;
-
-	const [branchList, forkList] = await Promise.all([
-		listBranches(gitTarget(parent.publicConfig, parent.repo, event.fetch), BRANCH_LIMIT)
-			.then((page) => page.branches ?? [])
-			.catch(() => [] as BranchEntry[]),
-		viewerDid
-			? listRepos(ctx, viewerDid, { limit: 100 })
-					.then((page) =>
-						page.items
-							// `source` is any uri: an at-uri means a fork, anything else is
-							// an import, same test the repo layout's resolveSource makes
-							.filter(
-								(item) =>
-									item.value.source?.startsWith("at://") && item.value.repoDid
-							)
-							.map((item): ForkOption => ({
-								uri: item.uri,
-								repoDid: item.value.repoDid as string,
-								name: repoNameOf(item),
-								knot: item.value.knot
-							}))
-					)
-					.catch(() => [] as ForkOption[])
-			: Promise.resolve([] as ForkOption[])
-	]);
-
-	let fork = params.get("fork") ?? "";
-	if (source === "fork" && !fork && forkList.length === 1) fork = forkList[0].repoDid;
-	const forkRepo = forkList.find((entry) => entry.repoDid === fork);
-
-	let prefillError = "";
-	let forkBranches: BranchEntry[] = [];
-	if (source === "fork" && forkRepo) {
-		try {
-			const page = await listBranches(
-				gitTarget(
-					parent.publicConfig,
-					{ uri: forkRepo.uri, repoDid: forkRepo.repoDid },
-					event.fetch
-				),
-				BRANCH_LIMIT
-			);
-			forkBranches = sortBranchesByRecency(page.branches ?? []);
-		} catch (cause) {
-			prefillError = cause instanceof Error ? cause.message : String(cause);
-		}
-	}
-
-	const sourceBranches = sourceBranchChoices(branchList);
-	const targetBranch = defaultTargetBranch(branchList, params.get("targetBranch") ?? "");
-	const sourceBranch = defaultSourceBranch(
-		source,
-		params.get("sourceBranch") ?? "",
-		sourceBranches,
-		forkBranches
-	);
-
-	const sourceRepoDid = fork || repoDid;
-	const hasComparison = Boolean(sourceRepoDid && sourceBranch && targetBranch);
-
-	let commits: CommitSummary[] = [];
-	let commitsError = "";
-	if (hasComparison && source !== "patch") {
-		try {
-			const page = await listCommits(ctx, {
-				repo: sourceRepoDid as Did,
-				ranges: [`${targetBranch}..${sourceBranch}`],
-				limit: COMMIT_LIMIT
-			});
-			commits = page.commits.map(toMirrorCommitSummary);
-		} catch (cause) {
-			commitsError = cause instanceof Error ? cause.message : String(cause);
-		}
-	}
-
-	return {
-		commits,
-		commitsError,
-		sourceRepoPath: forkRepo
-			? `${parent.auth?.handle ?? parent.repo.ownerHandle}/${forkRepo.name}`
-			: `${parent.repo.ownerHandle}/${parent.repo.name}`,
-		branches: sortBranches(branchList.map(toBranchSummary)),
-		sourceBranches,
-		forkBranches,
-		forks: forkList,
-		source,
-		sourceBranch,
-		targetBranch,
-		fork,
-		patch: params.get("patch") ?? "",
-		sourceRepoDid,
-		sourceKnot: forkRepo?.knot ?? parent.repo.knot,
-		showDetails: hasComparison,
-		prefillError
-	};
 };
diff --git a/web/src/routes/login/+page.svelte b/web/src/routes/login/+page.svelte
index aa7bcd13b..ca0bceff9 100644
--- a/web/src/routes/login/+page.svelte
+++ b/web/src/routes/login/+page.svelte
@@ -12,6 +12,14 @@
 	const appPath = (path: string) => resolve(path as "/");
 	const auth = getAuth();
 	const returnTo = $derived(page.url.searchParams.get("return_url") ?? "/");
+	const banner = $derived.by(() => {
+		const code = page.url.searchParams.get("error");
+		if (code === "session") return "Your session expired. Sign in again.";
+		if (code === "access_denied") return "You have not authorized the app.";
+		if (code) return "Something went wrong signing in. Please try again.";
+		if (auth.state.kind === "failed") return `${auth.state.message} Please try again.`;
+		return null;
+	});
 
 	let identifier = $state(page.url.searchParams.get("identifier") ?? "");
 	const login = createAction(async (event: SubmitEvent) => {
@@ -44,7 +52,9 @@
 
 	<form class="mt-4" onsubmit={login.run}>
 		<div class="flex flex-col">
-			<label for="identifier" class="py-2 typography-paragraph-small text-foreground-default">Handle</label>
+			<label for="identifier" class="py-2 typography-paragraph-small text-foreground-default"
+				>Handle</label
+			>
 			<input
 				id="identifier"
 				bind:value={identifier}
@@ -59,8 +69,8 @@
 				class="w-full rounded-sm border border-border-default bg-background-default p-2 typography-paragraph-large text-foreground-default placeholder:text-foreground-placeholder focus:ring-1 focus:ring-border-strong focus:outline-none"
 			/>
 			<p class="mt-1 typography-paragraph-small text-foreground-subtle">
-				Use your <span class="text-foreground-default">AT Protocol</span> handle to log in. If
-				you're unsure, this is likely your Tangled
+				Use your <span class="text-foreground-default">AT Protocol</span> handle to log in.
+				If you're unsure, this is likely your Tangled
 				<code
 					class="rounded-sm bg-background-inset px-1 typography-monospace-small font-mono text-foreground-default"
 					>(.tngl.sh)</code
@@ -86,20 +96,21 @@
 	</form>
 
 	<p class="typography-paragraph-small text-foreground-subtle">
-		Don't have an account? <a href={appPath("/signup")} class="text-foreground-default underline"
-			>Create an account</a
+		Don't have an account? <a
+			href={appPath("/signup")}
+			class="text-foreground-default underline">Create an account</a
 		>
 		on Tangled now!
 	</p>
 
-	{#if auth.state.kind === "failed"}
+	{#if banner}
 		<div
 			class="my-2 flex gap-2 rounded-sm border border-border-danger bg-background-danger-subtle px-3 py-2 text-foreground-danger shadow-xs"
 		>
 			<span class="py-1" aria-hidden="true"><CircleAlert class="size-4" /></span>
 			<div>
 				<h5 class="font-medium">Login error</h5>
-				<p class="typography-paragraph-small">{auth.state.message} Please try again.</p>
+				<p class="typography-paragraph-small">{banner}</p>
 			</div>
 		</div>
 	{/if}
diff --git a/web/src/routes/strings/new/+page.svelte b/web/src/routes/strings/new/+page.svelte
index 58ccef538..ed0ba1a09 100644
--- a/web/src/routes/strings/new/+page.svelte
+++ b/web/src/routes/strings/new/+page.svelte
@@ -1,13 +1,9 @@
 <script lang="ts">
 	import { goto } from "$app/navigation";
-	import { getAuth } from "$lib/auth.svelte";
 	import StringForm from "$lib/components/strings/StringForm.svelte";
 
-	const auth = getAuth();
-	const user = $derived(auth.currentUser);
-
-	const handleSaved = async (rkey: string) => {
-		await goto(`/strings/${user?.handle}/${rkey}`);
+	const handleSaved = async (rkey: string, handle: string) => {
+		await goto(`/strings/${handle}/${rkey}`);
 	};
 </script>
 
@@ -18,7 +14,9 @@
 <div class="mx-auto w-full max-w-screen-lg px-4 py-12">
 	<div class="p-2">
 		<h1 class="typography-heading-4 font-bold text-foreground-default">Create a new string</h1>
-		<p class="typography-paragraph-small text-foreground-subtle">Store and share code snippets with ease.</p>
+		<p class="typography-paragraph-small text-foreground-subtle">
+			Store and share code snippets with ease.
+		</p>
 	</div>
 
 	<div class="mt-4">