release: v2.3.0 — image-baked fallback skills + opencode 1.17.10 + mempalace 3.5.0

- Add image-baked fallback skills (opencode-devbox-environment, mempalace) +
  harness instruction (instructions/opencode-devbox.md) under
  /usr/local/share/opencode-devbox/, symlinked in by entrypoint-user.sh
  (skills only-when-absent; instruction symlink to image, never copied into the
  devbox-opencode-config volume). Ported from pi-devbox v1.2.0/v1.2.1, adapted
  to opencode's ~/.config/opencode/instructions/ auto-load model. No
  pi-extensions skill (opencode has no fork/recall).
- Bump opencode 1.17.8 -> 1.17.10.
- Bump mempalace 3.4.0 -> 3.5.0 (lockstep with pi-devbox v1.2.2); remove the
  obsolete diary_write anyOf perl workaround (fixed upstream, issue #1728).
- Fix stale ssh-lan.conf ProxyJump guidance comment in setup-lan-access.sh
  (mirrors pi-devbox 8de0fad); comment-only.
- smoke-test.sh + recreate-sanity-check.sh assert baked source + resolved links.
- Docs: README Custom skills, AGENTS.md duties + MINOR example, CHANGELOG.

AGENTS.md

@@ -18,7 +18,7 @@ Docker image packaging [opencode](https://opencode.ai) into a production-ready d
 - `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 installs gated by build args: `INSTALL_OPENCODE` (default true), `INSTALL_OMOS`, and `INSTALL_MEMPALACE`. All GitHub-sourced binaries are pinned with version ARGs. Two variants: `base` (`INSTALL_OPENCODE=true`) and `omos` (`+INSTALL_OMOS=true`).
 - `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.
-- `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`), a one-time npm-global prefix migration shim (legacy `~/.pi/npm-global` → `~/.config/opencode/npm-global`), skillset auto-deploy from mounted skillset repo, OMOS bundled-skills reconcile (symlinks the image's bundled skills into `~/.agents/skills/`), OMOS config setup.
+- `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`), a one-time npm-global prefix migration shim (legacy `~/.pi/npm-global` → `~/.config/opencode/npm-global`), skillset auto-deploy from mounted skillset repo, OMOS bundled-skills reconcile (symlinks the image's bundled skills into `~/.agents/skills/`), image-baked fallback-skills reconcile (symlinks `/usr/local/share/opencode-devbox/skills/*` into `~/.agents/skills/` only-when-absent) + harness-instruction reconcile (symlinks `/usr/local/share/opencode-devbox/instructions/*.md` into `~/.config/opencode/instructions/`), OMOS config setup.
 - `rootfs/usr/local/lib/opencode-devbox/setup-lan-access.sh` — host-OS-agnostic LAN reachability helper. Always writes the writable `~/.ssh-local/config` sidecar on **every** host OS: a `Host *` block that redirects `ControlPath` into `~/.ssh-local/cm/` (first-value-wins over any read-only `~/.ssh`-bound per-host setting) plus `Include ~/.ssh/config`. On VM-backed hosts (macOS OrbStack / Docker Desktop, detected via `host.docker.internal` resolution) it additionally inserts the host-jump block; on native Linux that block is omitted (LAN is reachable directly) but the sidecar is still rendered. Previously the script exited early on native Linux, leaving `dssh`/`dscp` broken when `~/.ssh` was read-only there. Controlled by `DEVBOX_LAN_ACCESS` / `HOST_SSH_USER` / `DEVBOX_HOST_ALIAS` / `DEVBOX_LAN_AUTOJUMP_PRIVATE`. Ships the mechanism only (generic `host` jump alias); user targets stay host-side — named-peer `ProxyJump host` overrides go in a bind-mounted `~/.config/devbox-shell/ssh-lan.conf` (Included before `~/.ssh/config`), never baked into the image. **Scoping invariant:** every `Include` in the generated config MUST be preceded by a bare `Host *` reset — an `Include` is scoped to the enclosing `Host`/`Match` block, so without the reset the included config only applies when targeting `host`/`mac` and named peers fall back to SSH defaults. Non-fatal. Counted in the base hash, so editing it advances `base-latest`.
 - `rootfs/usr/local/lib/opencode-devbox/generate-config.py` — generates `~/.config/opencode/opencode.jsonc` from env vars. Never overwrites an existing config (checks both `.json` and `.jsonc`). Auto-registers MCP servers for detected tools (mempalace via `mempalace-mcp`, gitea-mcp, context7 remote endpoint).
 - `scripts/smoke-test.sh` — post-build image verification. Asserts binary presence, opencode startup, entrypoint correctness, config generation idempotency, and image size thresholds. Used by both CI workflows.
@@ -45,7 +45,8 @@ repo, which decoupled from the pi tool version at its own `v1.0.0`.
   reference example.
 - **MINOR** — backward-compatible features: new variants/tags, new opt-in
   behavior, new env vars, or changed-but-compatible semantics. Example: `v2.1.0`
-  added the OMOS bundled-skills image-symlink mechanism.
+  added the OMOS bundled-skills image-symlink mechanism; `v2.3.0` added the
+  image-baked fallback skills + harness-instruction mechanism.
 - **PATCH** — opencode/tool version bumps and small fixes that don't change the
   contract. When a release pairs a tool bump with a feature, the feature wins
   and it's a minor.