CI: preventative fix for PI_VERSION/OMOS_VERSION cache-hit silent regression

Mirrors the pi-devbox v0.75.5b fix (2026-05-23) onto the four-variant
pipeline here. The with-pi, omos, and omos-with-pi variants install
upstream npm packages whose *_VERSION build-args defaulted to 'latest'.
When the build-arg string is byte-identical across builds, the layer
hash is identical and the registry buildcache silently reuses the layer
from whatever upstream version was current when the cache was first
populated — same mechanism that shipped pi-devbox v0.74.0..v0.75.5 with
identical image bytes.

Currently masked here because OPENCODE_VERSION is a hard-coded ARG that
bumps every release; parent-chain cache invalidation flushes the
downstream pi/omos layers. Masking would fail on any vN.N.Nb opencode-
version-unchanged release that only bumps pi or omos. Filed last night
as parked followup; fixing preventatively now that #5 (AWS SSO inside
tor-ms22 container) cleared.

CHANGES

.gitea/workflows/docker-publish-split.yml — new resolve-versions job
running 'npm view @earendil-works/pi-coding-agent version' and
'npm view oh-my-opencode-slim version', exposing concrete strings as
job outputs. All six affected jobs (smoke-omos, smoke-with-pi,
smoke-omos-with-pi, build-variant-omos, build-variant-with-pi,
build-variant-omos-with-pi) now consume them as PI_VERSION /
OMOS_VERSION build-args. smoke-base / build-variant-base unaffected.

scripts/smoke-test.sh — new run_expect helper asserting an expected
substring in command output. The pi check uses EXPECTED_PI_VERSION;
the omos check uses EXPECTED_OMOS_VERSION against npm ls -g. Both env
vars are wired from resolve-versions outputs in the smoke jobs. Catches
this regression class on the next release, not four releases later.

Dockerfile.variant — comment blocks above OPENCODE_VERSION (source-
pinned, not subject to the bug), PI_VERSION (CI-resolved), and
OMOS_VERSION (CI-resolved) explaining the cache-hit footgun.

AGENTS.md — new convention bullet under 'Critical conventions' naming
the resolve-versions job + EXPECTED_*_VERSION wiring as the contract
to keep in lockstep when modifying variant build-args.

.gitea/README.md — Step 1 expanded to cover the parallel resolve-
versions job alongside base-decide; pipeline diagram updated.

CHANGELOG.md — Unreleased entry describing the fix, masking mechanism,
and audit footprint.

No image-content change expected on the next release vs what 'latest'
would have resolved to anyway. Purely makes the cache invalidate
correctly going forward.

AGENTS.md

@@ -72,6 +72,7 @@ cd /tmp && npm pack @earendil-works/pi-coding-agent@0.75.5 && tar -xzf earendil-
   **Between releases the same coupling applies.** Doc drift is not just a release-day concern — a workflow tweak, entrypoint change, or `generate-config.py` refactor can leave any of these four files lying. Before committing a non-release change, grep the docs for references to what you touched: `git diff --name-only HEAD | xargs -I{} grep -l 'thing-you-changed' README.md AGENTS.md DOCKER_HUB.md .gitea/README.md .env.example`. If a doc says "four variants" / "two phases" / "runs on amd64 only" and your change made that no longer true, fix it in the same commit.
 - **GitHub/Gitea-sourced binaries float by default** — gosu, fzf, git-lfs, nvim, bat, eza, zoxide, uv, gitea-mcp, Go, oh-my-opencode-slim all default to `latest`. Each build-time install step reads the `/releases/latest` Location redirect (or the go.dev JSON feed for Go) and derives the concrete version. Use the same `ARCH` case-switch pattern for multi-arch support (amd64/arm64). Intentional pins: `OPENCODE_VERSION` (drives the image tag), `NODE_VERSION=22` (major pin), `DEBIAN_VERSION=trixie-slim` (OS base). Adding a new upstream tool: follow the existing floated-version pattern, don't hardcode a specific tag.
 - **Resolved versions are logged by the smoke test** — `scripts/smoke-test.sh` prints a "Resolved component versions" table as its first step. CI logs always capture what got baked into a given image even when ARGs default to `latest`.
+- **`PI_VERSION` and `OMOS_VERSION` MUST be passed by CI as concrete versions**, not left at the `latest` default. The npm install steps in `Dockerfile.variant` (`npm install -g @earendil-works/pi-coding-agent` / `oh-my-opencode-slim@${OMOS_VERSION}`) produce identical layer-hashes when the ARG values are byte-identical across builds; combined with the registry buildcache (`base-buildcache`) the layer gets reused even when `latest` would have resolved to a newer upstream. This is the same class of bug that bit pi-devbox v0.74.0 → v0.75.5 (silent same-bytes-across-releases regression discovered 2026-05-23, fixed in pi-devbox v0.75.5b). It is currently *masked* in opencode-devbox by `OPENCODE_VERSION` being a hard-coded ARG that bumps every release — that bump invalidates the parent-chain cache key for the downstream pi/omos layers — but the masking would fail the moment a `vN.N.Nb` opencode-version-unchanged release ships that only bumps pi or omos. Preventative fix: `.gitea/workflows/docker-publish-split.yml` has a `resolve-versions` job that runs `npm view @earendil-works/pi-coding-agent version` and `npm view oh-my-opencode-slim version`, exposing concrete values as outputs that every variant smoke + build job consumes via build-args. Smoke tests assert via `EXPECTED_PI_VERSION` / `EXPECTED_OMOS_VERSION` env vars — would catch the regression on the next release rather than four releases later. **If you change the variant build-args list, the resolve-versions job, or the smoke EXPECTED_*_VERSION wiring, audit all affected jobs in lockstep.**
 - **Shell scripts use `set -euo pipefail`** — both entrypoints are strict. Errors in volume chown or SSH permission operations are intentionally suppressed with `|| true`.
 - **MemPalace install path** — installed via `uv tool install` into `/opt/uv-tools/mempalace/`. Both the `mempalace` CLI and the `mempalace-mcp` MCP server binary are shipped as entry points by the mempalace package itself and placed on PATH by uv as shims whose shebangs point at the venv's Python. No hand-rolled wrapper is needed. Do not use `pip install --break-system-packages` — that was the previous approach and has been removed. Do not use `["python3", "-m", "mempalace.mcp_server"]` in `opencode.jsonc` — system Python can't import from the uv venv.
 - **generate-config.py idempotency** — the script MUST never overwrite an existing `opencode.jsonc` or legacy `opencode.json`. Config persists in the `devbox-opencode-config` named volume; accidentally clobbering that file would destroy hand-edits. The smoke test asserts this.