Merge branch 'code-runtime-worker' into code-mode-tools

Brings in the refreshed base (master merged through the stack after #203
and #205 landed), including the acp-snapshot extraction (#204), and
re-ports this PR's snapshot-suite extensions onto the extracted package:

- dsh-acp-snapshot's Scenario gains headerClass and configPath; the suite
  factory pins the request header PER CLASS (construction rejects a
  missing or duplicated class pin), forwards a scenario's configPath to
  the harness (RunOptions.configPath overrides AgentUnderTest.configPath),
  and a new fixtures meta-test asserts every pinning fixture carries
  exactly one request/header and no deltas.
- The acp-agent example's thin scenario table re-registers code-mode-turn
  and both-mode-turn with their overlay configs and per-class pins; the
  committed fixtures replay unchanged.
- The package's synthetic suites cover the new surface (explicit
  headerClass on one suite, the default on the other, a configPath
  override through the fake bin, and the two construction throws).

docs/rfc/INDEX.md

@@ -11,6 +11,8 @@ Generated by `pnpm run gen-rfc-index` from the RFC tree — never edit by hand;
 | [Agent Client Protocol (ACP) support — drive the coding agent from external editors](proposed/feature/2026-06-14-acp-agent-client-protocol.md) | 2026-06-14 |
 | [Multiplex concurrent ACP sessions over one connection](proposed/feature/2026-06-14-acp-multi-session.md) | 2026-06-14 |
 | [Pre-tool input rewrite — a consistent design](proposed/feature/2026-06-30-pre-tool-input-rewrite.md) | 2026-06-30 |
+| [Claude Code and Codex subagent backends (out-of-process delegation to external coding agents)](proposed/feature/2026-07-07-claude-code-and-codex-subagent-backends.md) | 2026-07-07 |
+| [Repeat-tool-call guard plugin](proposed/feature/2026-07-08-repeat-tool-guard.md) | 2026-07-08 |
 
 ### Simplification
 
@@ -164,6 +166,7 @@ Generated by `pnpm run gen-rfc-index` from the RFC tree — never edit by hand;
 | [Hook snapshot matrix — end-to-end goldens for both bridges](implemented/testing/2026-07-04-hook-snapshot-matrix.md) | 2026-07-04 |
 | [Single-source the acp-agent replay config](implemented/testing/2026-07-04-single-source-acp-replay-config.md) | 2026-07-04 |
 | [Pin request-header content in one snapshot scenario](implemented/testing/2026-07-06-pin-request-header-content-in-one-scenario.md) | 2026-07-06 |
+| [Extract the ACP snapshot suite into a support package](implemented/testing/2026-07-08-shared-acp-snapshot-package.md) | 2026-07-08 |
 
 ## Rejected