docs(docker): warn that a plain agent-image rebuild keeps stale CLIs

The CLIs live in one `RUN npm install -g` layer, so rebuilding without
--no-cache re-uses it and freezes them at the versions the image was FIRST
built with. Editing the Dockerfile does not help when the edit lands below
that line: the npm layer stays cached and only the new step runs.

That is not hypothetical. Adding the Antigravity step (which appends below
the npm line) produced a "successful" rebuild that silently kept a stale
@openai/codex@0.144.6 whose aliased platform binary had never installed, so
every codex docker case died with "Missing optional dependency
@openai/codex-linux-x64" while the build reported success. A --no-cache
rebuild fixed codex and also un-froze claude, gemini and opencode.

Documents the failure, makes --no-cache the recommended invocation in both
the guide and the CLAUDE.md quick-reference row, and adds a verify command
that actually executes each CLI, since a zero exit code only proves the
layers ran.

No changeset: docs-only, rides the next release.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -102,7 +102,7 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 | Test coverage                  | `npm run test:coverage`                                                                                                                                                                                        |
 | Dead-code sweep                | `npm run knip` (config in `config/knip.json`, passed via `--config`)                                                                                                                                          |
 | Rebuild gesture overlay        | `npm run build:gesture` (esbuild `packages/gesture-control/src/codeman/entry.ts` → `src/web/public/gesture/gesture-codeman.js`; commit the result)                                                             |
-| Build the docker agent image   | `node scripts/build-agent-image.mjs` (builds `codeman/agent:base` from `docker/agent.Dockerfile`; prerequisite for Docker cases; `--engine`/`--image`/`--no-cache`)                                            |
+| Build the docker agent image   | `node scripts/build-agent-image.mjs --no-cache` (builds `codeman/agent:base` from `docker/agent.Dockerfile`; prerequisite for Docker cases; `--engine`/`--image`). ⚠ **Always `--no-cache`** — a plain rebuild re-uses the cached `npm install -g` layer and silently keeps the CLIs frozen at their original versions, which once shipped a BROKEN codex while reporting success. See `docs/docker-cases.md` |
 | Gesture playground             | `npm run dev` **in** `packages/gesture-control/` (standalone vite demo, fake tabs)                                                                                                                             |
 | Check public-asset formatting  | `npm run check:public-assets` (prettier-checks `src/web/public/**` text assets; `scripts/check-public-assets.mjs`)                                                                                             |
 | Frontend JS syntax check       | `npm run check:frontend-syntax` (`scripts/check-frontend-syntax.mjs`; runs in CI)                                                                                                                              |

docs/docker-cases.md

@@ -15,6 +15,21 @@ node scripts/build-agent-image.mjs          # builds codeman/agent:base
 
 The image is **secret-free**: credentials are delivered at runtime (bind mounts or `docker exec --env`), never baked in, so exports never leak them.
 
+⚠️ **Re-build with `--no-cache`, always.** The CLIs are installed in a single `RUN npm install -g` layer, so a plain rebuild re-uses it from the Docker layer cache and the CLIs stay frozen at whatever versions the image was **first** built with, however long ago that was. Editing the Dockerfile does not help unless the edit lands at or above that line: a change appended below it leaves the npm layer cached and only runs the new step. Observed 2026-08-06: a rebuild silently kept a stale `@openai/codex@0.144.6` whose aliased platform binary had not installed, so every `codex` docker case died with `Missing optional dependency @openai/codex-linux-x64` while the build itself reported success.
+
+```bash
+node scripts/build-agent-image.mjs --no-cache
+```
+
+A zero exit code only proves the layers ran, not that the toolchain works. Verify by actually executing each CLI in the image, and check the build log for `Using cache` lines:
+
+```bash
+docker run --rm codeman/agent:base bash -lc \
+  'for c in claude codex gemini opencode agy; do printf "%-9s " $c; $c --version 2>&1 | head -1; done'
+```
+
+Antigravity (`agy`) is the one CLI not installed from npm (Google ships a standalone binary), so it has its own Dockerfile step and adds roughly 190MB; a full image lands near 1.6GB.
+
 ## Quickest path: one-click "Run in Docker"
 
 On the **New case → Create New** tab there's a **🐳 Run in an isolated Docker container** checkbox. Checking it alone is enough: Codeman creates the case folder in `~/codeman-cases/<name>`, spins up a hardened container with sensible defaults (auto-provisioning a shared `default` host), and starts the session inside it. No host/image/network fields to fill in.