From fc3f402ee95efcde54106386e84c48881fdb978a Mon Sep 17 00:00:00 2001
From: onevcat <onevcat@gmail.com>
Date: Tue, 21 Jul 2026 22:31:28 +0900
Subject: [PATCH] Make resume-fork side-effect-free for the source session

Claude Code's `--resume` defaults to continuing the same session ID, so a
headless preparation appended turns to the transcript of a session still
live in the pane. `--fork-session` forks the preparation turn onto a new
ID; Codex `--ephemeral` keeps it out of ~/.codex/sessions entirely.

Claude-Session: https://claude.ai/code/session_01EtBU9JYAcRp3nUuPfGH3n8
---
 .../AgentRuntime/AgentRuntimeAdapter.swift      | 17 ++++++++++++-----
 supacodeTests/AgentRuntimeAdapterTests.swift    |  4 +++-
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/supacode/Domain/AgentRuntime/AgentRuntimeAdapter.swift b/supacode/Domain/AgentRuntime/AgentRuntimeAdapter.swift
index 48b55164..39ed6d0d 100644
--- a/supacode/Domain/AgentRuntime/AgentRuntimeAdapter.swift
+++ b/supacode/Domain/AgentRuntime/AgentRuntimeAdapter.swift
@@ -7,9 +7,11 @@ nonisolated protocol AgentRuntimeAdapter: Sendable {
 
   func observe(arguments: [String]) -> AgentLaunchObservation
   func makeStartInvocation(_ request: AgentStartRequest) throws -> AgentInvocation
-  /// Resume is read-only by design: the invocation never renders execution-mode
-  /// flags. The resumed agent replies with content; Prowl persists any artifact.
-  /// `replyFile`, when supported, asks the CLI to write its final message there.
+  /// Resume is side-effect-free by design: the invocation never renders
+  /// execution-mode flags, and it must not mutate the source session's recorded
+  /// state (fork/ephemeral variants only). The resumed agent replies with
+  /// content; Prowl persists any artifact. `replyFile`, when supported, asks the
+  /// CLI to write its final message there.
   func makeResumeInvocation(_ request: AgentResumeRequest, replyFile: URL?) throws -> AgentInvocation
 }
 
@@ -178,7 +180,9 @@ nonisolated private struct CodexRuntimeAdapter: AgentRuntimeAdapter {
   }
 
   func makeResumeInvocation(_ request: AgentResumeRequest, replyFile: URL?) throws -> AgentInvocation {
-    var arguments = ["exec", "resume"]
+    // `--ephemeral` keeps the preparation turn out of `~/.codex/sessions`, so a
+    // resume never mutates the recorded state of the live source session.
+    var arguments = ["exec", "resume", "--ephemeral"]
     if let model = request.model {
       arguments += ["--model", model]
     }
@@ -223,7 +227,10 @@ nonisolated private struct ClaudeCodeRuntimeAdapter: AgentRuntimeAdapter {
 
   func makeResumeInvocation(_ request: AgentResumeRequest, replyFile: URL?) throws -> AgentInvocation {
     // `claude -p` prints only the final reply on stdout, so no reply file is needed.
-    var arguments = ["-p", "--resume", request.session.id]
+    // `--fork-session` is load-bearing: without it `--resume` continues the same
+    // session ID and appends the preparation turn to the transcript of a session
+    // that is usually still live in the pane (dual-writer on one JSONL).
+    var arguments = ["-p", "--fork-session", "--resume", request.session.id]
     if let model = request.model {
       arguments += ["--model", model]
     }
diff --git a/supacodeTests/AgentRuntimeAdapterTests.swift b/supacodeTests/AgentRuntimeAdapterTests.swift
index 8a993c10..7f5b525f 100644
--- a/supacodeTests/AgentRuntimeAdapterTests.swift
+++ b/supacodeTests/AgentRuntimeAdapterTests.swift
@@ -43,6 +43,7 @@ struct AgentRuntimeAdapterTests {
       invocation.arguments
         == [
           "-p",
+          "--fork-session",
           "--resume",
           "9B0E3B0E-67B3-4D45-A3A0-7DD9BC713711",
           "--model",
@@ -76,6 +77,7 @@ struct AgentRuntimeAdapterTests {
         == [
           "exec",
           "resume",
+          "--ephemeral",
           "--model",
           "gpt-5.4",
           "--output-last-message",
@@ -187,7 +189,7 @@ struct AgentRuntimeAdapterTests {
     #expect(reply == "## Objective\nreply")
     #expect(recordedExecutable.value?.path == "/usr/bin/env")
     let arguments = recordedArguments.value
-    #expect(arguments.prefix(3) == ["codex", "exec", "resume"])
+    #expect(arguments.prefix(4) == ["codex", "exec", "resume", "--ephemeral"])
     #expect(arguments.contains("--output-last-message"))
     #expect(!arguments.contains("--dangerously-bypass-approvals-and-sandbox"))
     #expect(
-- 
2.51.2