feat(tools): one static /mcp endpoint, session chosen by bearer key - #44

…ok (#49)

* feat(tools): wire the tools MCP into the CLI from an image startup hook (#39)

The runtime keeps knowing no coding CLI's config format. Instead it gains one
generic seam, `--startup-hook <FILE>`: an image-provided executable it runs
once, after seeding and before serving, best-effort (failure, non-zero exit or
a 30 s timeout is logged and serving continues). After seeding matters: a seed
archive may carry the very config file the hook edits.

The images ship deploy/hooks/startup-hook.sh (bash + jq; jq added to both
Dockerfiles). For kiro-cli, when PTY_TOOLS_LISTEN is set, it writes #44's
session-independent form into ~/.kiro/settings/mcp.json:

  computer = { url: http://<PTY_TOOLS_LISTEN>/mcp,
               headers: { Authorization: "Bearer ${OPENAB_TOOLS_MCP_TOKEN}" } }

and adds @computer/* to allowedTools in existing agent files. No session name
or key is ever on disk, so one shared workspace config serves every session
and survives every key rotation. With the tools plane off, only the entry the
hook wrote is withdrawn. A new CLI is a function in the hook, not a runtime
change.

Merge rules come from #45: other servers/settings preserved, wrong-shaped or
malformed files left byte-identical, agent files never created, dangling
symlinks left alone, atomic writes that keep the file's mode. Changed from
#45: no stdio JS bridge (superseded by #44's header route), restrictive
`tools` lists and `mcpServers` in agent files are not touched, key order is
kept, and the knowledge lives in the image rather than the runtime.

Closes #39. Supersedes #45.

Co-authored-by: Reese-max <198568376+Reese-max@users.noreply.github.com>

* fix(hook): scrub the hook's env, kill and reap its group, respect user entries

Review round 1 on #49.

- B1: the hook ran with the runtime's full environment while jq loaded
  ~/.jq from the shared workspace, so a planted ~/.jq could write e.g. an
  ECS credentials URI into a config the next session reads. The hook now
  gets env_clear() + the session allowlist + OPENAB_PTY_TOOLS_LISTEN, and
  the script runs jq with HOME=/nonexistent.
- S1: the hook leads its own process group; on exit or timeout the group
  is SIGKILLed and reparented members are reaped (waitpid(-pgid)), so no
  orphan or zombie outlives it.
- S2: main.rs documents why the exec'd, dumpable hook is safe (scrubbed
  env, no session yet). Inline step numbers fixed.
- S3: the hook runs after the binds and is handed the tools address the
  runtime actually bound (same as OPENAB_TOOLS_MCP_ENDPOINT), not
  PTY_TOOLS_LISTEN re-read from env. IPv6 tested.
- S4: tools-on replaces `computer` only when absent, ours (by header), or a
  hand-wired URL on this listener; anything else is left with a warning.
- S5: a failed temp-file write is never renamed over the config.
- Nits: non-regular paths and multi-document files left alone; HOME unset
  exits 0; "*" in allowedTools counts as trusted; WaitFailed outcome;
  jq version noted in the Dockerfile; `jq --version` in CI; tests for all
  of the above (39 shell cases, 8 hook tests incl. children and background
  members). Test-only ETXTBSY retry for scripts exec'd right after writing.

* fix(hook): never fatal on a JoinError, tolerate non-UTF-8 env at boot

Review round 2 nits on #49.

- A failed spawn_blocking task (panic inside it) was propagated with `?`,
  contradicting the hook's best-effort contract; it is now a warning.
- std::env::vars() panics on a non-UTF-8 variable, which with
  --startup-hook would have aborted the runtime at boot. Use vars_os()
  and drop variables that are not UTF-8 (the allowlist is ASCII anyway).

Verified: runtime started with BAD=\xff\xfe in its env and a hook, hook
ran and saw OPENAB_PTY_TOOLS_LISTEN, runtime kept serving.

---------

Co-authored-by: Reese-max <198568376+Reese-max@users.noreply.github.com>