feat: bake OPENCODE_EXPERIMENTAL_BACKGROUND_SUBAGENTS=true (base ENV)

opencode gates native background subagents behind this experimental flag;
oh-my-opencode-slim V2+ makes background orchestration its default workflow,
so the omos variant was effectively degraded without it. Set as a base-level
ENV (both variants, harmless for plain opencode) and overridable at runtime.

Documented in lockstep: README env table, .env.example, CHANGELOG Unreleased,
and AGENTS.md (with a removal trigger for when opencode promotes it out of
experimental). smoke-test asserts the var is baked into the image env.

Also folds the prior CLI-tools additions into the CHANGELOG Unreleased block.

AGENTS.md

@@ -108,6 +108,7 @@ curl -s https://api.github.com/repos/anomalyco/opencode/releases/tags/v1.15.10 |
 - **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 + 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`.
+- **Background subagents flag baked ON — experimental, watch for promotion** — `Dockerfile.base` sets `ENV OPENCODE_EXPERIMENTAL_BACKGROUND_SUBAGENTS=true`. opencode gates native background subagents behind this flag (`packages/opencode/src/tool/task.ts` fails with `Background subagents require OPENCODE_EXPERIMENTAL_BACKGROUND_SUBAGENTS=true` when unset); `oh-my-opencode-slim` V2+ makes background orchestration its **default** workflow, so the omos variant is effectively degraded without it. It's a base ENV (applies to both variants; harmless on plain opencode — only *enables* a capability) and stays runtime-overridable (`-e …=false`). It's counted in the base hash, so editing that line advances `base-latest`. **REMOVAL TRIGGER:** when opencode promotes background subagents out of `EXPERIMENTAL_` (flag renamed or made default), drop the ENV. No upstream roadmap date as of opencode 1.17.15 / omos 2.1.0 (2026-07). Documented in lockstep in README env table, `.env.example`, and asserted by `scripts/smoke-test.sh` (`bg-subagents env baked`).
 - **MemPalace `diary_write` anyOf workaround — upstream watch target** — `Dockerfile.base` carries a perl RUN block that strips a root-level `anyOf` from `mempalace_diary_write`'s advertised `inputSchema`. Mempalace 3.3.x/3.4.0 advertise `anyOf: [{required:[entry]},{required:[content]}]`, which Anthropic's tools API (and Codex) reject at session start (`input_schema does not support oneOf, allOf, or anyOf at the top level`), making the whole MCP server fail to load. The workaround is idempotent and self-deactivating: when upstream ships the real fix the regex stops matching and the build prints `WARN: ... upstream may have changed shape` — **that WARN is the signal to delete the RUN block.** Upstream status (last checked **2026-06-14**): issue **#1728 is still OPEN**; PR **#1735 is CLOSED UNMERGED (2026-06-11) — do NOT watch it, it is dead**; PR **#1717 is the current live fix candidate**; mempalace PyPI latest is **3.4.0 (== our pin)**, so **no release contains the fix yet** and the workaround must stay. **Removal trigger:** a mempalace release **> 3.4.0** that actually strips the root-level `anyOf` lands on PyPI — then bump `MEMPALACE_VERSION` (in lockstep with pi-devbox) and drop the RUN block. NOTE: `MEMPALACE_VERSION` (the pip pin) and `MEMPALACE_TOOLKIT_REF` (the git ref for the `mempalace-toolkit` clone) are unrelated despite the shared prefix; do not conflate them.
 - **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.