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/module-graph.md

@@ -68,6 +68,7 @@ flowchart TD
     pkg_session_persistence_sqlite["session-persistence-sqlite"]
   end
   subgraph group_support["packages/support"]
+    pkg_acp_snapshot["acp-snapshot"]
     pkg_invariants["invariants"]
     pkg_llm_replay["llm-replay"]
     pkg_subagent_mock["subagent-mock"]
@@ -216,6 +217,7 @@ flowchart TD
 | Package | Group | Depends on |
 | --- | --- | --- |
 | [`brand`](../packages/util/brand) | `util` | — |
+| [`acp-snapshot`](../packages/support/acp-snapshot) | `support` | — |
 | [`app-boot`](../packages/ui/app-boot) | `ui` | — |
 | [`code-runtime`](../packages/code-runtime/code-runtime) | `code-runtime` | — |
 | [`llm`](../packages/llm/llm) | `llm` | [`brand`](../packages/util/brand) |