[Birfy]

Closes #896

#892 taught the CLI to accept latest/last, but show_payload / status_payload / apply_payload and the MCP tools that call them (or runstore directly) still looked up a directory named latest. A host asked to "show the latest run" got no run 'latest'.

• agentdescent/cli.py: extract resolve_run_id and use it from the payload helpers (and the CLI wrapper).
• agentdescent/diagnose.py: report the resolved run id after show_payload.
• agentdescent/mcp.py: resolve on cancel/resume; document latest/last on the tool descriptions.
• tests/test_latest_run_alias.py: payload + MCP coverage, including the empty-store wording.
• changelog.d/896-mcp-latest-run-alias.md.

Tests: pytest tests/test_latest_run_alias.py tests/test_changelog_fragments.py tests/test_mcp.py tests/test_diagnose.py pass locally.

[Birfy]

Verdict: PASS
Tip SHA: 0872b4c

Ran: pytest -q tests/test_latest_run_alias.py tests/test_changelog_fragments.py tests/test_mcp.py tests/test_diagnose.py at the tip → passed. risk_gate.py from main → T2 (118 changed lines / 5 files).
Not run: full suite (CI covers 3.9–3.13).

Correctness. #892 swapped latest/last only in CLI main() before the command ran. show_payload / status_payload / apply_payload (and MCP Tools.show/status/apply/diagnose, which call them) still looked up a directory named latest; MCP cancel/resume hit runstore the same way. resolve_run_id is now the shared helper: a real directory named latest still wins, an empty store keeps the #892 wording, and diagnose_payload reports the resolved id from show_payload. Tool descriptions mention the alias so hosts know they can pass it.

Tests / docs. Extended tests/test_latest_run_alias.py for payload helpers and MCP tools (including empty-store errors). Changelog fragment 896-mcp-latest-run-alias.md.

Risk. T2 (package code: cli.py, mcp.py, diagnose.py + tests + changelog). AGENT_PAUSE=false; will squash-merge when required CI is green.