docs: fix drift against main batch (SSH sidecar, proposed config, provenance, forked build)

DRIFT-STALE fixes (stale/misleading text corrected):
- README.md:160 — "on native Linux it does nothing" → accurate always-render
  description (sidecar written on every OS; jump block still omitted on Linux)
- AGENTS.md:22 — setup-lan-access.sh "no-op on native Linux" → corrected to
  always-render + removed now-redundant inline ControlPath/UserKnownHostsFile
  sentence (that's what the sidecar does, not what the script detects)
- CHANGELOG.md:594 (v2.1.1 intro) — "no-op" → "(see v2.2.0)" historical note
- docs/plan-lan-access-and-pi-extensions.md:222 — annotated the completed
  checkbox with the v2.2.0 refinement

GAP additions:
- README.md:212 — custom config section now describes opencode.jsonc.proposed
  sidecar: written-on-diff, removed-on-match, never overwrites, one-line hint
- README.md build-args table — INSTALL_MEMPALACE_TOOLKIT row now mentions
  MEMPALACE_TOOLKIT_REPO alongside MEMPALACE_TOOLKIT_REF
- README.md (after build-args table) — two new sections:
    "Building a fork / relocated build" — MEMPALACE_TOOLKIT_REPO build-arg
    table + two-step docker build example + credentials note
    "Build provenance (labels + manifest)" — docker inspect + run examples,
    OCI label set, ground-truth manifest path

Version string drift: no hard-coded 1.17.7 found outside CHANGELOG (all
occurrences are historical release entries — correct by definition).
CI-internal items (resolve-versions, check-base-hash.sh): no existing doc
described these mechanics, so no update needed.

AGENTS.md

@@ -19,7 +19,7 @@ Docker image packaging [opencode](https://opencode.ai) into a production-ready d
 - `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.
-- `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` / `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. The top `Host *` block also overrides `UserKnownHostsFile` and `ControlPath` into the writable `~/.ssh-local` sidecar (first-value-wins), because the bind-mounted `~/.ssh` is read-only — otherwise multiplexed hosts (`ControlPath ~/.ssh/cm/...`) fail to create their master socket. Non-fatal. Counted in the base hash, so editing it advances `base-latest`.
+- `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.
 - `scripts/recreate-sanity-check.sh` — **runtime** post-recreate verification (counterpart to the build-time `smoke-test.sh`). Run inside the container after `docker compose up -d --force-recreate` to confirm the new image is live (opencode version matches `Dockerfile.variant`'s `OPENCODE_VERSION`), persisted named volumes survived (mempalace palace, opencode.db, bash-history), omos runtime skill symlinks resolve, shell defaults re-seeded, and `/opt` toolkits intact. Not run by CI or the entrypoint — it needs the running container + volumes that smoke-test.sh (which uses `--entrypoint=""`) cannot see.