[Iris] Add babysitting MCP server

[dlwh]

Add a marin-mcp-babysitter entry point with resident Iris controller/log clients, structured job/task/log/worker/process/profile tools, Zephyr progress parsing, and diagnosis signals. Also documents MCP-assisted babysitting in the job monitoring skill after live smoke validation.

Part of #5018

[claude]

Claude finished @dlwh's task in 8m 14s —— View job

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Code review

• Check PR status and whether review is needed
• Gather CLAUDE.md/AGENTS.md files relevant to changed files
• Read PR changes and summarize
• Run 4 parallel review agents (2 AGENTS.md compliance, 2 bug-finding)
• Validate each flagged issue via subagents
• Filter high-signal findings
• Post inline comments and summary

Found 2 high-signal issues, posted as inline comments:

1. _jobs_with_prefix uses raw startswith (comment) — a tree rooted at /alice/train pulls in string-prefix siblings like /alice/train-v2/... into nodes, even though they're correctly excluded from children by the JobName.is_ancestor_of check later. Consumers iterating nodes directly see jobs that don't belong to the tree. Suggest filtering in _jobs_with_prefix (or before inserting into nodes) using the JobName hierarchy.

2. --iris-token CLI flag leaks the bearer token via ps//proc and bypasses the Iris token-store pattern (comment) — every other Iris CLI goes through create_client_token_provider → load_token(cluster_name) / load_any_token() (from iris login). Recommend using the same lookup path here instead of a --token flag.

Investigated and dismissed (to save reviewer time): tautological-test framing of test_classify_diagnosis_* (it does assert behavior per input pattern, just doesn't cover severity/evidence/escalation_hint); multi-line parsing in zephyr_stage_progress (coordinator emits one progress record per line); theoretical orphaning in job_tree (no job-deletion path in the controller DB today); _s/_ms suffix complaints (rule only bans the bare _s abbreviation); _profile_type "duplication" (the iris version is inline in a Click command, not an extractable helper — no parallel implementation to violate).
· Branch: agent/20260421-fix-5018

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[dlwh]

🤖 Live MCP smoke test passed on marin-dev. I submitted /dlwh/mcp-babysitter-smoke-20260422-1017, ran marin-mcp-babysitter over streamable HTTP, and verified iris_job_summary plus iris_tail_logs through the MCP endpoint. The job printed mcp-babysitter-smoke tick=<n> roughly every 30s through tick=59, emitted mcp-babysitter-smoke done, and finished with state=succeeded, failure_count=0, preemption_count=0, and no error.

[yonromai]

Haven't done MCP in ages, but LGTM!

[rjpower]

nit: https://googleapis.dev/python/protobuf/latest/google/protobuf/json_format.html

will do this automatically?

[dlwh]

🤖 Follow-up PR for the protobuf json_format review nit: #5071