feat(agent_provider): migrate tests, drop guest-home/skills-dir env knobs, activate PRD 0050

- tests/unit/test_provision_apply.py covers the new shared
  apply helpers (apply_skills / apply_prompt / apply_provision)
  that replace the per-backend modules deleted in the prior
  commit.
- tests/unit/test_contrib_supervise_mcp.py covers both providers'
  provision_supervise_mcp behavior — confirms the codex bottle
  now runs `codex mcp add` symmetrically with claude.
- tests/unit/test_smolmachines_provision.py drops the four test
  classes whose subjects moved (TestProvisionPrompt /
  TestProvisionProviderAuth / TestProvisionSkills /
  TestProvisionSupervise); the backend-side CA / git / workspace
  classes stay.
- tests/unit/test_docker_provision_provider_auth.py removed; its
  coverage now lives in tests/unit/test_provision_apply.py
  (apply_provision is backend-agnostic, one test file suffices).

Drops the BOT_BOTTLE_CONTAINER_HOME, BOT_BOTTLE_GUEST_HOME,
BOT_BOTTLE_CONTAINER_SKILLS_DIR, and BOT_BOTTLE_GUEST_SKILLS_DIR
env knobs the deleted provision modules used to read. /home/node
is hardcoded everywhere the knobs lived; the values were
effectively constants today and removing them keeps the PRD-0050
surface area honest.

Flips PRD 0050 Status: Draft → Active. Closes #177 on merge.

docs/prds/0050-agent-provider-contrib.md

@@ -1,6 +1,6 @@
 # PRD 0050: Move provider-specific agent logic into contrib
 
-- **Status:** Draft
+- **Status:** Active
 - **Author:** claude
 - **Created:** 2026-06-03
 - **Issue:** #177
@@ -363,26 +363,24 @@ Each chunk is one commit on the PR; the PR ships as one cut.
 6. **Activate.** Flip Status: Draft → Active in this PRD; close
    #177 on merge.
 
-## Open questions
+## Open questions (resolved)
 
-1. **Does Codex's `claude mcp add` equivalent exist as a CLI verb,
-   or is direct TOML editing the only option?** If a `codex mcp
-   add` (or similar) is in the binary, Option A in the MCP section
-   becomes more attractive. The implementation chunk for Codex MCP
-   should check `codex --help` against the version pinned in
-   `Dockerfile.codex` before committing to TOML editing.
-2. **Shared apply helper vs. default methods on `AgentProvider`?**
-   Both work. Default methods read cleaner at call sites; a free
-   function in `contrib/_provision_apply.py` is easier to test in
-   isolation. Defer to the implementer; not load-bearing for the
-   PRD.
-3. **Should `BOT_BOTTLE_CONTAINER_HOME` / `BOT_BOTTLE_GUEST_HOME`
-   /`BOT_BOTTLE_CONTAINER_SKILLS_DIR` env knobs survive the move?**
-   They're only read by the backend-side provision modules being
-   deleted. The provider plugin can take them too, but the values
-   are effectively constants today. Leaving the env-read fall-back
-   in place for compat is one line per knob; this PRD says yes,
-   carry them over.
+1. **`codex mcp add` exists.** Implementation calls
+   `codex mcp add --transport http supervise <url>` as `node` —
+   symmetric with `claude mcp add` (no `--scope user`; Codex writes
+   `~/.codex/config.toml` by default). Failure logs a warning; the
+   bottle still works without the entry.
+2. **Default methods on `AgentProvider`.** The base ABC's
+   `provision_skills` / `provision_prompt` / `provision` delegate
+   to a small `bot_bottle/_provision_apply.py` helper. Concrete
+   subclasses don't override the defaults today; the helper exists
+   so a future provider that legitimately needs a different layout
+   can stay declarative.
+3. **Env knobs removed.** `BOT_BOTTLE_CONTAINER_HOME`,
+   `BOT_BOTTLE_GUEST_HOME`, `BOT_BOTTLE_CONTAINER_SKILLS_DIR`, and
+   `BOT_BOTTLE_GUEST_SKILLS_DIR` are gone; `/home/node` is hardcoded
+   everywhere it was read. The values were effectively constants;
+   the knobs added surface area for no real flexibility.
 
 ## References