Summary

Closes the CLI gap left by PR-D C1a (#628), which lifted wiki/override.py:render_seed_bytes for agents / commands but shipped no CLI to drive them. Users now have a symmetric surface across all three asset types:

mm wiki skill   override <name> --vendor <claude|gemini|codex>
mm wiki agent   override <name> --vendor <claude|gemini|codex>
mm wiki command override <name> --vendor <claude|gemini|codex>

Vendor renderers report which canonical fields they cannot represent (gemini agents drop skills/isolation; gemini commands drop argument-hint/allowed-tools/model); the new CLI surfaces those via stderr warning: so the user editing the override knows what the runtime won't see.

Series position (ADR-0008 PR-D)

Why two commits

The plan splits the work along a refactor / new-feature axis so each commit is a working, reviewable unit:

• 0cc705d refactor — extract _run_seed_override helper for override CLI. Three call sites are about to share a body, so the YAGNI window for the helper is open now. wiki/override.py grows a SeedResult(path, dropped) dataclass, and render_seed_bytes / seed_override propagate the renderer's dropped list (C1a silently discarded it). skill_override_cmd collapses to the helper. The five known errors collapse into one except (...) tuple — verified disjoint via inheritance grep (WikiNotFoundError / OverrideExistsError / NotImplementedError → RuntimeError; FileNotFoundError → OSError; InvalidNameError → ValueError).
• e313da5 feat — mm wiki {agent,command} override + dropped-fields warning. Two new wiki.group blocks, each with an override subcommand that delegates to the helper. The helper now exercises the dropped-fields stderr branch (skills always have dropped == []; agents / commands populate it depending on vendor). ("commands", "codex") keeps its permanent placeholder behaviour — seed_override raises NotImplementedError and the helper surfaces it as a classified ClickException rather than a Python traceback.

Collapse safety gate

feedback_pre_collapse_parity_grep pattern: surviving path's invariants are pinned before / during the N→1 collapse. Skills had ten existing CLI tests (all assert on result.output, the combined stream), so a silent regression where the new dropped-fields warning fired for skills would not surface. Commit 1 adds test_wiki_skill_override_no_stderr_warning, which uses result.stderr == "" (Click 8.3 keeps result.stderr separate by default — earlier mix_stderr=False constructor arg was removed) to pin the four-axis invariant for skills:

The first three were already pinned before this PR; the fourth is the new collapse-specific gate.

Test surface

• test_wiki_override.py 4 / 4 pass. Two pin tests (*_for_agents_uses_vendor_generator, *_for_commands_uses_vendor_generator) unpack the new tuple shape and assert dropped == [] for the minimal canonical fixtures (no vendor-uncovered fields → no drops). The other two are exception-only and unchanged.
• test_wiki_cmd_override.py 32 / 32 pass:
  • 10 existing skill tests (PR-C feat(context): PR-C — wiki override + agent/command install widening (ADR-0008) #624) — unchanged behaviour after the helper collapse.
  • 1 new test_wiki_skill_override_no_stderr_warning (commit 1 safety gate).
  • 10 agent mirror tests covering happy path / dropped warning / refuse / force / unknown vendor / missing agent / missing wiki / editor / no-editor / stdout contract.
  • 11 command mirror tests covering the same plus test_wiki_command_override_codex_classified_error (the permanent placeholder pin).
• Full suite: uv run pytest packages/memtomem/tests/ -m "not ollama" -q → 3475 pass, 46 deselected (ollama), +22 over C1a's 3453 (1 safety gate + 21 mirror).
• Lint: ruff check + ruff format --check clean across packages/memtomem/src + packages/memtomem/tests.

Manual smoke (mode 2 isolation, MEMTOMEM_WIKI_PATH override)

=== gemini agent → stderr warning ===
warning: vendor 'gemini' will not represent these fields: skills, isolation
PASS: warning, skills, isolation, stdout summary

=== claude agent → stderr empty ===
PASS: stderr empty, stdout summary

=== codex command → classified error, no traceback ===
exit 1; stderr: Error: 'codex' commands not yet supported — see OVERRIDE_FORMATS placeholder
PASS: non-zero exit, classified message, no traceback

=== gemini command → stderr warning + .toml extension ===
warning: vendor 'gemini' will not represent these fields: argument-hint, allowed-tools, model
PASS: warning, argument-hint, allowed-tools, model, .toml extension

Out of scope (subsequent PRs)

• mm wiki <type> {edit, diff, lint} — defined in ADR-0008 §Subcommands but C1b is explicitly override-only.
• mm context update / status / install --all / migrate — C2 / C3 / C4.

Test coverage gap (follow-up)

• Codex agents drop set (tools / skills / isolation / kind / temperature) is exercised only through the shared helper path, not via a vendor-specific fixture. Gemini agents (skills / isolation) and gemini commands (argument-hint / allowed-tools / model) cover the warning code path; codex agents share that same path so the marginal regression-detection value is low. Add a codex-specific fixture when generator drop sets change or as part of a vendor-coverage cleanup PR — not C2 scope, since C2's dirty detection deals with file mtime, not vendor renderer drops.

Post-review fixup

• 0a114df fixup(c1b): newline guard in test fixture helpers — _seed_agent / _seed_command now normalise frontmatter_extra to end with a trailing \n. Current call sites already do this; the guard prevents a future fixture from silently producing a malformed YAML frontmatter (closing --- merging into the previous line). Test-only impact, +12 / -2 lines.

Test plan

• uv run pytest packages/memtomem/tests/test_wiki_cmd_override.py packages/memtomem/tests/test_wiki_override.py -v — 36 pass.
• uv run pytest packages/memtomem/tests/ -m "not ollama" -q — 3475 pass.
• uv run ruff check packages/memtomem/src packages/memtomem/tests — clean.
• uv run ruff format --check packages/memtomem/src packages/memtomem/tests — clean.
• Manual mode-2 smoke — 4 / 4 pass.
• CI green (waiting).

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