feat: add pi-only variant (pi without opencode) as basis for pi-devbox

All opencode-devbox variants set INSTALL_OPENCODE=true, so pointing pi-devbox
at with-pi dragged opencode along and made it ~a re-tag of latest-with-pi.
Add a 5th variant pi-only (INSTALL_OPENCODE=false, INSTALL_PI=true): pi +
companions (toolkit, extensions, fork, recall) + base tooling, no opencode
(~145 MB lighter than with-pi).

- Dockerfile.variant: document pi-only in the variant table.
- CI docker-publish-split.yml: new smoke-pi-only + build-variant-pi-only jobs
  (tags :VERSION-pi-only / :latest-pi-only, multi-arch); wired into
  promote-base-latest and update-description needs.
- validate.yml: new validate-pi-only main-branch gate job.
- smoke-test.sh: accept --variant pi-only; threshold 2750 MB; opencode-absent
  path already handled.
- Docs: HUB_TEMPLATE (regenerated DOCKER_HUB.md), README, AGENTS (variant/tag
  counts 4->5, 8->10 tags), .gitea/README, manual-host-publish.sh (5 variants),
  plan doc implementation note.

This is the single source of truth for joakimp/pi-devbox, which now FROMs
latest-pi-only. Versions unchanged (opencode 1.15.13, pi 0.78.0).

AGENTS.md

@@ -7,7 +7,7 @@ Docker image packaging [opencode](https://opencode.ai) into a production-ready d
 ## File roles
 
 - `Dockerfile.base` — variant-independent layers (apt, locales, AWS CLI, Node.js, mempalace, gitea-mcp, user setup, chromadb prewarm, ENVs, entrypoints). Published as `joakimp/opencode-devbox:base-<sha12>`. Rebuilt only when its content hash changes.
-- `Dockerfile.variant` — `FROM`s the base and adds only opencode/omos/pi installs gated by build args: `INSTALL_OPENCODE` (default true), `INSTALL_OMOS`, `INSTALL_PI`, and `INSTALL_MEMPALACE`. All GitHub-sourced binaries are pinned with version ARGs. When `INSTALL_PI=true` it also clones `pi-fork` + `pi-observational-memory` (from `github.com/elpapi42`, refs `PI_FORK_REF`/`PI_OBSMEM_REF`) to `/opt` and runs `npm install` there at build time so the `fork`/`recall` extensions can load (a local-path `pi install` does not npm-install).
+- `Dockerfile.variant` — `FROM`s the base and adds only opencode/omos/pi installs gated by build args: `INSTALL_OPENCODE` (default true), `INSTALL_OMOS`, `INSTALL_PI`, and `INSTALL_MEMPALACE`. All GitHub-sourced binaries are pinned with version ARGs. When `INSTALL_PI=true` it also clones `pi-fork` + `pi-observational-memory` (from `github.com/elpapi42`, refs `PI_FORK_REF`/`PI_OBSMEM_REF`) to `/opt` and runs `npm install` there at build time so the `fork`/`recall` extensions can load (a local-path `pi install` does not npm-install). The `pi-only` variant sets `INSTALL_OPENCODE=false`, `INSTALL_PI=true` — pi without opencode, the single source of truth for the separate `pi-devbox` image.
 - `entrypoint.sh` — runs as root: UID/GID adjustment, SSH permissions, volume ownership fixes (skipped via `.devbox-owner` sentinel when ownership is already correct). Then drops to developer via gosu. Volume ownership loop covers `~/.pi/` when `INSTALL_PI=true`.
 - `entrypoint-user.sh` — runs as developer: git config, opencode.jsonc generation (delegated to `generate-config.py`), LAN-access setup (delegated to `setup-lan-access.sh`), pi-toolkit + pi-extensions deploy (when pi installed), pi settings.json bootstrap, mempalace pi-bridge symlink, runtime `pi install /opt/{pi-fork,pi-observational-memory}` registration (idempotent), skillset auto-deploy from mounted skillset repo, OMOS setup.
 - `rootfs/usr/local/lib/opencode-devbox/setup-lan-access.sh` — host-OS-agnostic LAN reachability helper. Detects VM-backed hosts (macOS OrbStack / Docker Desktop, via `host.docker.internal` resolution) and generates a writable `~/.ssh-local/config` using the host as an SSH jump; no-op on native Linux. Controlled by `DEVBOX_LAN_ACCESS` / `HOST_SSH_USER` / `DEVBOX_HOST_ALIAS`. Ships the mechanism only (generic `host` jump alias); user targets stay in their bind-mounted `~/.ssh/config`. Non-fatal. Counted in the base hash, so editing it advances `base-latest`.
@@ -18,7 +18,7 @@ Docker image packaging [opencode](https://opencode.ai) into a production-ready d
 - `README.md` — authoritative source documentation for everything in this repo. Independent of `DOCKER_HUB.md`: the Hub doc is hand-maintained in the generator's `HUB_TEMPLATE` and intentionally slim, linking back to the gitea README for depth.
 - `.gitea/README.md` — **read this first** if you're touching CI. Architectural overview of the build pipeline (production vs split-base), wall-clock estimates, NPM_CONFIG_PREFIX gotcha, runner expectations, migration plan.
 - `.gitea/workflows/validate.yml` — lightweight amd64 build + smoke test on push to main and PRs. Also runs the DOCKER_HUB.md sync check.
-- `.gitea/workflows/docker-publish-split.yml` — production CI pipeline on tag push (`v*`). Two-phase split-base: computes base hash, conditionally builds base, runs 4 parallel smoke tests, then 4 parallel multi-arch variant builds, promotes `base-latest` alias, updates Docker Hub description.
+- `.gitea/workflows/docker-publish-split.yml` — production CI pipeline on tag push (`v*`). Two-phase split-base: computes base hash, conditionally builds base, runs 5 parallel smoke tests, then 5 parallel multi-arch variant builds, promotes `base-latest` alias, updates Docker Hub description.
 
 ## Versioning scheme
 
@@ -36,7 +36,7 @@ Tags follow `v{opencode_version}[letter]` — e.g. `v1.14.20` for the first buil
   
   Cautionary example: 2026-05-28 morning, `v1.15.12` was cut while opencode-ai was still at `1.15.11`. The commit message itself acknowledged "OPENCODE_VERSION stays at 1.15.11" but tagged `v1.15.12` anyway. Re-cut as `v1.15.11c` the same afternoon (see CHANGELOG). The `v1.15.12` git tag and Hub images stayed as historical artifacts; the slip cost a CI cycle and a CHANGELOG-rewrite. **Run the npm view check at the top of every release-day cut.**
 
-CI produces eight Docker Hub tags per release: `vX.Y.Z[n]`, `latest`, `vX.Y.Z[n]-omos`, `latest-omos`, `vX.Y.Z[n]-with-pi`, `latest-with-pi`, `vX.Y.Z[n]-omos-with-pi`, `latest-omos-with-pi` — one tag pair (versioned + floating alias) per build variant.
+CI produces ten Docker Hub tags per release: `vX.Y.Z[n]`, `latest`, `vX.Y.Z[n]-omos`, `latest-omos`, `vX.Y.Z[n]-with-pi`, `latest-with-pi`, `vX.Y.Z[n]-omos-with-pi`, `latest-omos-with-pi`, `vX.Y.Z[n]-pi-only`, `latest-pi-only` — one tag pair (versioned + floating alias) per build variant (five variants).
 
 When bumping the opencode version, bump `OPENCODE_VERSION` in `Dockerfile.variant` and update the comment in `.env.example` if it names a specific model/version for context.
 
@@ -82,7 +82,7 @@ cd /tmp && npm pack @earendil-works/pi-coding-agent@0.75.5 && tar -xzf earendil-
 - **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.**
 - **Registry buildkit cache-export is currently disabled** — do NOT re-add `cache-from`/`cache-to` to the `build-base` step in `.gitea/workflows/docker-publish-split.yml` without first verifying that buildkit's `mode=max` cache-export to `registry-1.docker.io` no longer returns HTTP 400 from the Hub CDN edge. The regression surfaced ~2026-05-23 and broke five consecutive opencode-devbox publish attempts (runs #332/333/334/336 + a rerun); root-caused on 2026-05-28 by a manual host-side publish that reproduced the same 400 only on `--cache-to` while image push worked fine. Failure shape is stable (`Offset:0` in the `_state` token, HTML response body = CDN-tier rejection, not registry backend), repo-specific (we're the only repo writing `:base-buildcache` mode=max), and explains why pinning `setup-buildx-action@v4.0.0` didn't help (action pin doesn't change the bundled buildkit version on the catthehacker runner image). Trade-off: dockerfile.base changes pay a full ~3 min rebuild instead of pulling cached layers; unchanged bases short-circuit at the Hub-probe step in `base-decide` and never re-build anyway. Variants don't use registry cache so they're unaffected. Re-enable condition: upstream moby/buildkit fix lands AND a low-risk test run succeeds without 400s. See CHANGELOG v1.15.12 `Unreleased` block for the full diagnostic chain. Manual escape-hatch publish procedure: `docs/manual-host-publish.md`.
-- **Push steps wrap `docker buildx build --push` in a 3-attempt retry loop** (15s, 30s backoff) for transient `registry-1.docker.io` blips — rate limits, brief 5xx, CDN flap. Implemented as inline `shell: bash` steps with `docker buildx build` raw rather than `docker/build-push-action@v7` so the loop is visible and tweakable. Affects the 1 base + 4 variant push steps in `.gitea/workflows/docker-publish-split.yml`; smoke-test builds (`load: true`, no push) are untouched. **This does NOT mask deterministic failures** — a true regression (like the cache-export 400 of 2026-05-23..28) fails all 3 attempts identically and the job still fails. Orthogonal to the cache-export disablement above: cache-export was about a deterministic protocol mismatch, retry is about absorbing genuine transients. Both are belt-and-braces with the `ci-release-watcher` skill's transient-rerun heuristic. If you change the matrix of push steps, keep the retry wrapper consistent across them — the pattern is duplicated rather than factored out because Gitea Actions doesn't support reusable composite shell steps cleanly.
+- **Push steps wrap `docker buildx build --push` in a 3-attempt retry loop** (15s, 30s backoff) for transient `registry-1.docker.io` blips — rate limits, brief 5xx, CDN flap. Implemented as inline `shell: bash` steps with `docker buildx build` raw rather than `docker/build-push-action@v7` so the loop is visible and tweakable. Affects the 1 base + 5 variant push steps in `.gitea/workflows/docker-publish-split.yml`; smoke-test builds (`load: true`, no push) are untouched. **This does NOT mask deterministic failures** — a true regression (like the cache-export 400 of 2026-05-23..28) fails all 3 attempts identically and the job still fails. Orthogonal to the cache-export disablement above: cache-export was about a deterministic protocol mismatch, retry is about absorbing genuine transients. Both are belt-and-braces with the `ci-release-watcher` skill's transient-rerun heuristic. If you change the matrix of push steps, keep the retry wrapper consistent across them — the pattern is duplicated rather than factored out because Gitea Actions doesn't support reusable composite shell steps cleanly.
 - **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.