docs: reference only helpers that exist on main (AGENTS.md)

Review caught a real forward-reference: the new AGENTS.md section named
`ltDiag` and told readers to wait on `closed`, and NEITHER exists on main —
both are introduced by the still-unmerged #204. `git grep ltDiag` matched
exactly one line: the documentation itself.

That is worse than a broken link. AGENTS.md is, by its own "Handoff
expectations", the FIRST file a fresh session reads; it would have sent that
session looking for two identifiers it cannot find, in the file whose whole job
is to orient them.

It also meant this PR had an undeclared merge-order dependency on #204, which
I had not stated anywhere.

Fixed so each PR is self-consistent regardless of merge order:
  - names `ltPostStatus` (which does exist) instead of `ltDiag`
  - states the #203 rule as a PRINCIPLE — a terminated child's pipes may still
    hold unread data, so wait for stdio to close rather than for the exit —
    instead of naming the `closed` flag that #204 adds

Verified: every helper the section now names resolves to a `function <name>` in
test-features.mjs on this branch, and neither `ltDiag` nor `closed` is
referenced any more.

Tests: 457 passed, 0 failed (comments/docs only, unchanged).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017gbqUZ8HfBZpjjbzQ85oH8

AGENTS.md

@@ -52,6 +52,22 @@ Runtime: Node.js (ESM, `.mjs` throughout). No build step. No bundler. `server.mj
 
 ---
 
+## Testing: reaching faults inside `server.mjs`
+
+`test-features.mjs` cannot `import` `server.mjs` (it calls `server.listen()` at top level), and that has twice led to the wrong conclusion that a class of bug is untestable. It isn't. Read this before writing "no regression test is possible here".
+
+**There is a real live-server fixture.** `ltBoot(env, dir, nodeArgs)` (around `test-features.mjs:990`) spawns the actual `server.mjs` as a child with a **fake `claude` binary**, so integration tests cost no quota. `ltPost` / `ltPostStatus` / `ltWait` / `ltFreePort` round it out. It already covers boot gates, cache-epoch invalidation across two boots sharing one SQLite store, and system-prompt capture.
+
+**`--stack-size` is a fault lever.** `ltBoot`'s third argument passes V8 flags to the child, which puts recursion- and argument-count-limited failures in reach at a much smaller input. `#193` needed a *synchronous throw* deep inside `spawnClaudeProcess`; `buildCliArgs` does `args.push("--allowedTools", ...ALLOWED_TOOLS)`, and under `--stack-size=200` that spread throws at ~24k elements instead of ~124k — which is what brings the trigger under Linux's `MAX_ARG_STRLEN` (131072 bytes for a single env string) so the test runs in CI rather than skipping. **No production fault hook was needed.**
+
+Three rules that made it hold up, all learned the hard way:
+
+- **Discover the threshold in a child under the same flags**, never in the test process — the parent's stack is not the one that matters.
+- **Assert that the fault actually fired**, not just that the outcome looks right. `#193` asserts HTTP 500 *and* that the body carries `call stack size exceeded`; a control mutation (trigger neutered, bug still present) proves the test fails rather than passing vacuously.
+- **Wait for the thing you are about to assert**, not a proxy for it. Waiting on `listening on` and then asserting a different line is a race (`#199`); waiting for the process to *exit* and then reading its `stderr` is another, because a terminated child's pipes may still hold unread data (`#203` — wait for the stdio to close, not for the exit).
+
+Allocate ports with `ltFreePort()`. Fixed ports have caused at least one flake here.
+
 ## Release protocol
 
 OCP follows the machine-readable `release_kit:` overlay in `CLAUDE.md` (Iron Rule 5.5). Before any version bump or tag push, re-read that YAML block and walk every item in `new_feature_doc_expectations` and `bootstrap_quirk_policy`. Tag push triggers `.github/workflows/release.yml`, which creates the GitHub Release automatically — do not create the release manually.

server.mjs

@@ -2923,6 +2923,16 @@ async function handleChatCompletions(req, res) {
     const t0s = Date.now();
     const promptCharsS = messages.reduce((a, m) => a + contentToText(m.content).length, 0);
     let structuredHash = null;
+    // DO NOT collapse this with `dedupKey` below (#200). The two cacheHash calls take IDENTICAL
+    // arguments and look like obvious duplicate work — they are not interchangeable, because
+    // their GUARDS differ: this one additionally requires CACHE_TTL > 0. CLAUDE_CACHE_TTL
+    // DEFAULTS TO 0, so in the default configuration structuredHash is null while dedupKey must
+    // still be computed — it drives #153's single-flight stampede protection, which is
+    // deliberately independent of whether response caching is on. `dedupKey = structuredHash`
+    // would therefore silently disable stampede protection by default, in exactly the
+    // concurrent-AI-Task case it exists to bound. The duplicate call is the honest price of the
+    // asymmetry. If you do deduplicate it, compute once under the WEAKER guard and derive the
+    // cache lookup under the stronger one — and add a stampede test before you do.
     if (CACHE_TTL > 0 && !conversationId && !hasCacheControl(messages)) {
       structuredHash = cacheHash(cacheModel, messages, { keyId: req._authKeyId, temperature: parsed.temperature, max_tokens: parsed.max_tokens, top_p: parsed.top_p, structured, configEpoch: CONFIG_EPOCH });
       try {
@@ -2942,6 +2952,8 @@ async function handleChatCompletions(req, res) {
     // firing several AI Tasks at once) must NOT each pay N× — they share one flight. We dedup every
     // one-off structured request (not stateful sessions / client-side prompt caching), independent of
     // whether OCP response caching is enabled; when caching IS on, the same key gates cache read/write.
+    // Note the guard here is deliberately WEAKER than structuredHash's — no CACHE_TTL check. See the
+    // do-not-collapse comment above (#200).
     const dedupKey = (!conversationId && !hasCacheControl(messages))
       ? cacheHash(cacheModel, messages, { keyId: req._authKeyId, temperature: parsed.temperature, max_tokens: parsed.max_tokens, top_p: parsed.top_p, structured, configEpoch: CONFIG_EPOCH })
       : null;