feat(grok): start the in-container SDK server + budget feed (Claude parity)

The keystone of the Grok parity work (CEO's "take Claude as baseline, create
what's missing" call): the one-shot Grok container now starts the same SDK
server the Claude path runs, so the per-verb circuit breaker (the flow/do MCP
servers already POST /verb/attempted to it), the per-session budget/loop
counters, the terminal-verb tracking, and the SessionEnd post-mortem all work
on Grok instead of being silently absent.

- entrypoint: launch roboco.agent_sdk.server (bare venv python, not `uv run`
  which would re-sync the drifted clone lock and stall), wait for /health,
  reset counters; run opencode WITHOUT exec so the script regains control to
  run the post-mortem and the silent-exit substitute after the run returns.
- budget-feed.js: opencode plugin that gates on /budget/status in
  tool.execute.before (halt/loop deny — the only place to stop a runaway
  one-shot run; opencode has no PostToolUse-deny) and records the executed
  tool + args-hash in tool.execute.after. Fail-open; bare-verb normalization
  for MCP-namespaced terminal verbs.
- silent-exit substitute: on a graceful exit with no terminal verb the
  entrypoint posts /terminal/force_substitute so the task isn't left stuck
  claimed/in_progress (Stop-hook parity at the boundary).
- opencode_config: wire budget-feed into the plugin array; add
  ROBOCO_OPENCODE_EXTRA_PLUGINS so per-image role tool plugins load scoped to
  one role; read the per-role ROBOCO_GROK_EDIT_PERMISSION.

Targeted gate green (ruff/mypy/xenon + opencode_config tests; node --check on
the plugins; bash -n on the entrypoint).

docker/agent-grok.Dockerfile

@@ -21,9 +21,13 @@ RUN npm install -g opencode-ai @ai-sdk/openai \
     && npm cache clean --force \
     && rm -rf /root/.npm /tmp/*
 
-# Command guard / secret-scrub plugin (bash-guard parity for the opencode runtime).
-# Referenced from the generated opencode.json `plugin:` array.
+# opencode plugins (referenced from the generated opencode.json `plugin:` array):
+#   secret-scrub — bash-guard parity (PAT/credential deny on tool.execute.before)
+#   budget-feed  — POSTs budget/loop/terminal counters to the in-container SDK
+#                  server (tool.execute.{before,after}); the entrypoint starts
+#                  that server (roboco.agent_sdk.server) for Claude-parity.
 COPY docker/grok/secret-scrub.js /app/opencode-plugins/secret-scrub.js
+COPY docker/grok/budget-feed.js /app/opencode-plugins/budget-feed.js
 
 # Entrypoint: render opencode.json, then run opencode (overrides base's `claude`).
 COPY docker/scripts/grok-agent-entrypoint.sh /app/scripts/grok-agent-entrypoint.sh