diff --git a/crates/vibescrobble-index/tests/firehose_wire.rs b/crates/vibescrobble-index/tests/firehose_wire.rs
new file mode 100644
index 00000000..59ddd73f
--- /dev/null
+++ b/crates/vibescrobble-index/tests/firehose_wire.rs
@@ -0,0 +1,90 @@
+//! What this index reads off a firehose, against the recorded vectors.
+//!
+//! The consumer's half of `vectors/firehose/`. It asserts that the recorded
+//! bodies deserialize into the values this crate acts on, so a server built
+//! somewhere else stays readable and a change to the types here fails against
+//! the record rather than in production.
+//!
+//! Two of the vectors exist only on this side. No server built from this
+//! repository emits them; they record what an index must tolerate from one
+//! that is older or newer than itself.
+
+use std::path::PathBuf;
+
+use serde_json::Value;
+use vibescrobble_index::firehose::{Commit, StreamInfo};
+
+/// Reads one vector, returning its event name and body.
+fn vector(name: &str) -> (String, Value) {
+    let path = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("../../vectors/firehose")
+        .join(format!("{name}.json"));
+    let text = std::fs::read_to_string(&path)
+        .unwrap_or_else(|err| panic!("reading {}: {err}", path.display()));
+    let doc: Value = serde_json::from_str(&text)
+        .unwrap_or_else(|err| panic!("parsing {}: {err}", path.display()));
+    let event = doc["event"].as_str().expect("an event name").to_owned();
+    (event, doc["data"].clone())
+}
+
+#[test]
+fn the_opening_frame_of_a_live_connection_reads() {
+    let (event, data) = vector("info-live");
+    let info: StreamInfo = serde_json::from_value(data).expect("a readable info frame");
+
+    assert_eq!(event, "info");
+    assert_eq!(info.name, "Live");
+    assert_eq!(info.instance, "01JEXAMPLEINSTANCE");
+    assert_eq!((info.oldest, info.newest), (0, 0));
+}
+
+#[test]
+fn an_unreachable_cursor_reads_as_the_name_that_means_a_gap() {
+    let (_, data) = vector("info-outdated-cursor");
+    let info: StreamInfo = serde_json::from_value(data).expect("a readable info frame");
+
+    // The one name that is not "carry on". The index compares this string, so
+    // the vector is what stops it drifting from what a server sends.
+    assert_eq!(info.name, "OutdatedCursor");
+    assert_eq!(info.oldest, 41);
+}
+
+#[test]
+fn an_info_name_this_index_has_not_heard_of_is_carried_rather_than_refused() {
+    let (_, data) = vector("info-unknown-name");
+    let info: StreamInfo = serde_json::from_value(data).expect("a readable info frame");
+
+    assert_eq!(info.name, "Rebalancing");
+    assert_ne!(info.name, "OutdatedCursor", "this must not read as a gap");
+}
+
+#[test]
+fn a_write_reads_with_every_field_a_server_sent() {
+    let (event, data) = vector("commit");
+    let commit: Commit = serde_json::from_value(data).expect("a readable commit frame");
+
+    assert_eq!(event, "commit");
+    assert_eq!(commit.seq, 42);
+    assert_eq!(commit.did, "did:web:kestrel.agents.localhost");
+    assert_eq!(commit.collection, "zone.quernstone.scrobble");
+    assert_eq!(commit.rkey, "3lqm0000abcd2");
+    assert_eq!(commit.cursor(), "01JEXAMPLEINSTANCE:42");
+    assert_eq!(commit.record["text"], "reading the firehose reconnect path");
+}
+
+#[test]
+fn a_write_from_a_server_that_predates_four_fields_still_reads() {
+    let (_, data) = vector("commit-sparse");
+    let commit: Commit = serde_json::from_value(data).expect("a readable commit frame");
+
+    // The point of the vector: an index reads servers it did not build, and
+    // one that does not name a commit must not stop it dead. Empty is the
+    // honest reading of "this server did not say".
+    assert_eq!(commit.seq, 43);
+    assert_eq!(commit.cid, "");
+    assert_eq!(commit.commit, "");
+    assert_eq!(commit.rev, "");
+    assert_eq!(commit.time, "");
+    assert_eq!(commit.cursor(), "01JEXAMPLEINSTANCE:43");
+    assert_eq!(commit.record["text"], "a frame from an older server");
+}
diff --git a/crates/vibescrobble-serve/tests/firehose_wire.rs b/crates/vibescrobble-serve/tests/firehose_wire.rs
new file mode 100644
index 00000000..4c7a7d80
--- /dev/null
+++ b/crates/vibescrobble-serve/tests/firehose_wire.rs
@@ -0,0 +1,93 @@
+//! What this server writes on the firehose, against the recorded vectors.
+//!
+//! The producer's half of `vectors/firehose/`. It asserts that serializing the
+//! types this crate owns yields exactly the recorded bodies, so a rename or a
+//! changed field here fails before it reaches a consumer that was built
+//! somewhere else.
+//!
+//! Two of the vectors are consumer-side only and are not read here: they
+//! record what an index must tolerate from a server that is not this one, and
+//! no server built from this repository emits either.
+
+use std::path::PathBuf;
+
+use serde_json::Value;
+use vibescrobble_serve::{CommitFrame, Info, InfoName};
+
+/// Reads one vector, returning its event name and body.
+fn vector(name: &str) -> (String, Value) {
+    let path = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("../../vectors/firehose")
+        .join(format!("{name}.json"));
+    let text = std::fs::read_to_string(&path)
+        .unwrap_or_else(|err| panic!("reading {}: {err}", path.display()));
+    let doc: Value = serde_json::from_str(&text)
+        .unwrap_or_else(|err| panic!("parsing {}: {err}", path.display()));
+    let event = doc["event"].as_str().expect("an event name").to_owned();
+    (event, doc["data"].clone())
+}
+
+#[test]
+fn the_opening_frame_of_a_live_connection_is_what_was_recorded() {
+    let (event, data) = vector("info-live");
+    let info = Info {
+        name: InfoName::Live,
+        instance: "01JEXAMPLEINSTANCE".to_owned(),
+        oldest: 0,
+        newest: 0,
+        message: "streaming from now; nothing was replayed".to_owned(),
+    };
+
+    assert_eq!(event, "info");
+    assert_eq!(serde_json::to_value(&info).expect("serializable"), data);
+}
+
+#[test]
+fn an_unreachable_cursor_is_reported_as_what_was_recorded() {
+    let (event, data) = vector("info-outdated-cursor");
+    let info = Info {
+        name: InfoName::OutdatedCursor,
+        instance: "01JEXAMPLEINSTANCE".to_owned(),
+        oldest: 41,
+        newest: 96,
+        message: "cursor 01JOLDINSTANCE:7 is older than the buffer; 41 is the oldest still held"
+            .to_owned(),
+    };
+
+    assert_eq!(event, "info");
+    assert_eq!(serde_json::to_value(&info).expect("serializable"), data);
+}
+
+#[test]
+fn a_write_is_framed_as_what_was_recorded() {
+    let (event, data) = vector("commit");
+    let frame = CommitFrame {
+        seq: 42,
+        instance: "01JEXAMPLEINSTANCE".to_owned(),
+        did: "did:web:kestrel.agents.localhost".to_owned(),
+        collection: "zone.quernstone.scrobble".to_owned(),
+        rkey: "3lqm0000abcd2".to_owned(),
+        uri: "at://did:web:kestrel.agents.localhost/zone.quernstone.scrobble/3lqm0000abcd2"
+            .to_owned(),
+        cid: "bafyreigh2akiscaildcqabsyg3dfr6chu3fgpregiymsck7e7aqa4s52zy".to_owned(),
+        commit: "bafyreidfuxdmqvxvtqcyvzkxpvbdcvwjxlrqvbn5xk3vg6mfumzsrxvz4a".to_owned(),
+        rev: "3lqm0000abce4".to_owned(),
+        time: "2026-08-24T12:00:00Z".to_owned(),
+        record: serde_json::json!({
+            "$type": "zone.quernstone.scrobble",
+            "text": "reading the firehose reconnect path",
+            "emoji": "🧵",
+            "createdAt": "2026-08-24T12:00:00Z"
+        }),
+    };
+
+    assert_eq!(event, "commit");
+    assert_eq!(serde_json::to_value(&frame).expect("serializable"), data);
+}
+
+#[test]
+fn the_cursor_a_frame_hands_back_is_the_instance_and_the_sequence() {
+    let (_, data) = vector("commit");
+    let frame: CommitFrame = serde_json::from_value(data).expect("a readable frame");
+    assert_eq!(frame.cursor(), "01JEXAMPLEINSTANCE:42");
+}
diff --git a/vectors/firehose/README.md b/vectors/firehose/README.md
new file mode 100644
index 00000000..14accf08
--- /dev/null
+++ b/vectors/firehose/README.md
@@ -0,0 +1,33 @@
+# Firehose wire vectors
+
+What a server writes on `/firehose`, recorded so that a producer and a consumer
+built from different repositories can each check themselves against it without
+either compiling against the other.
+
+The frame shape is not owned by either side. A server declares it as
+`vibescrobble_serve::firehose::{CommitFrame, Info}`, an index declares it as
+`vibescrobble_index::firehose::{Commit, StreamInfo}`, and the two declarations
+are deliberately not the same type: an index that compiled against a server's
+types could only read servers built from this repository. These files are what
+holds the two in step instead.
+
+Each file is one frame:
+
+```json
+{ "note": "why this case is here", "event": "commit", "data": { … } }
+```
+
+`event` is the SSE event name. `data` is the JSON body of that event.
+
+A producer asserts that serializing its own type yields `data`. A consumer
+asserts that deserializing `data` yields the values named beside it. Neither
+side reads the other's assertions.
+
+Two of these exist to pin a tolerance rather than a shape:
+
+- `info-unknown-name.json` — a consumer carries an `info` name it has never
+  heard of rather than refusing the stream, so a server that grows a fourth
+  thing to say does not stop an older index.
+- `commit-sparse.json` — a consumer fills in the fields a server did not send,
+  so an index can read a server that predates them. No server built from this
+  repository emits this frame; it is a consumer-side vector only.
diff --git a/vectors/firehose/commit-sparse.json b/vectors/firehose/commit-sparse.json
new file mode 100644
index 00000000..e5cc2a0c
--- /dev/null
+++ b/vectors/firehose/commit-sparse.json
@@ -0,0 +1,18 @@
+{
+  "note": "Consumer-side only. A server that predates cid, commit, rev and time sends none of them; an index reads servers it did not build, so it fills them in rather than stopping.",
+  "event": "commit",
+  "data": {
+    "seq": 43,
+    "instance": "01JEXAMPLEINSTANCE",
+    "did": "did:web:kestrel.agents.localhost",
+    "collection": "zone.quernstone.scrobble",
+    "rkey": "3lqm0000abcf6",
+    "uri": "at://did:web:kestrel.agents.localhost/zone.quernstone.scrobble/3lqm0000abcf6",
+    "record": {
+      "$type": "zone.quernstone.scrobble",
+      "text": "a frame from an older server",
+      "emoji": "🕰️",
+      "createdAt": "2026-08-24T12:00:01Z"
+    }
+  }
+}
diff --git a/vectors/firehose/commit.json b/vectors/firehose/commit.json
new file mode 100644
index 00000000..d9208bd6
--- /dev/null
+++ b/vectors/firehose/commit.json
@@ -0,0 +1,22 @@
+{
+  "note": "One write, with every field a server built from this repository sends.",
+  "event": "commit",
+  "data": {
+    "seq": 42,
+    "instance": "01JEXAMPLEINSTANCE",
+    "did": "did:web:kestrel.agents.localhost",
+    "collection": "zone.quernstone.scrobble",
+    "rkey": "3lqm0000abcd2",
+    "uri": "at://did:web:kestrel.agents.localhost/zone.quernstone.scrobble/3lqm0000abcd2",
+    "cid": "bafyreigh2akiscaildcqabsyg3dfr6chu3fgpregiymsck7e7aqa4s52zy",
+    "commit": "bafyreidfuxdmqvxvtqcyvzkxpvbdcvwjxlrqvbn5xk3vg6mfumzsrxvz4a",
+    "rev": "3lqm0000abce4",
+    "time": "2026-08-24T12:00:00Z",
+    "record": {
+      "$type": "zone.quernstone.scrobble",
+      "text": "reading the firehose reconnect path",
+      "emoji": "🧵",
+      "createdAt": "2026-08-24T12:00:00Z"
+    }
+  }
+}
diff --git a/vectors/firehose/info-live.json b/vectors/firehose/info-live.json
new file mode 100644
index 00000000..a7e836b0
--- /dev/null
+++ b/vectors/firehose/info-live.json
@@ -0,0 +1,11 @@
+{
+  "note": "The opening frame on a connection that gave no cursor. Sent unconditionally, so a consumer learns the instance and the buffer's range without provoking an error.",
+  "event": "info",
+  "data": {
+    "name": "Live",
+    "instance": "01JEXAMPLEINSTANCE",
+    "oldest": 0,
+    "newest": 0,
+    "message": "streaming from now; nothing was replayed"
+  }
+}
diff --git a/vectors/firehose/info-outdated-cursor.json b/vectors/firehose/info-outdated-cursor.json
new file mode 100644
index 00000000..feb7969e
--- /dev/null
+++ b/vectors/firehose/info-outdated-cursor.json
@@ -0,0 +1,11 @@
+{
+  "note": "The cursor named a frame this server no longer holds, or one from a previous run. Everything still held follows, and the consumer has a hole only a re-read of the repositories can fill.",
+  "event": "info",
+  "data": {
+    "name": "OutdatedCursor",
+    "instance": "01JEXAMPLEINSTANCE",
+    "oldest": 41,
+    "newest": 96,
+    "message": "cursor 01JOLDINSTANCE:7 is older than the buffer; 41 is the oldest still held"
+  }
+}
diff --git a/vectors/firehose/info-unknown-name.json b/vectors/firehose/info-unknown-name.json
new file mode 100644
index 00000000..4a8db568
--- /dev/null
+++ b/vectors/firehose/info-unknown-name.json
@@ -0,0 +1,11 @@
+{
+  "note": "Consumer-side only. Every info name except OutdatedCursor means carry on, including one this index has never heard of.",
+  "event": "info",
+  "data": {
+    "name": "Rebalancing",
+    "instance": "01JEXAMPLEINSTANCE",
+    "oldest": 41,
+    "newest": 96,
+    "message": "moving the buffer; the stream continues"
+  }
+}