Spec: repo-agnostic issue-planning MCP tool (draft-by-default, explicit create)

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Problem

generateContributorIssueDrafts (src/services/contributor-issue-draft.ts) already implements draft -> dedupe (stable HTML-comment marker + fingerprint) -> 30-day decline-cooldown -> create, but every one of its signal sources (repo policy readiness warnings, upstream registry drift, focus-manifest "wanted paths") and its create path are loopover-specific. Selfhosters need an equivalent that takes an arbitrary installed repo plus a maintainer-supplied planning goal and produces a structured issue plan they can review and optionally create against their own backlog.

Area

src/mcp/server.ts, src/services/contributor-issue-draft.ts (pattern to generalize), src/auth/security.ts.

Proposal

• New MCP tool registered in src/mcp/server.ts next to generateContributorIssueDrafts, in the same "Maintainer & repo owner" category, gated by requireRepoManageAccess (and the existing MCP_ACTUATION_REPO_ALLOWLIST check in src/auth/security.ts:169).
• Input: a target repo (must already have the App/Orb installed) plus free-form planning context (e.g. "plan issues for X feature area").
• Output: N structured issue drafts (title/body/labels), reusing contributor-issue-draft.ts's dedup/fingerprint-marker approach generalized to not assume loopover's own repo or its specific signal sources.
• Defaults to dryRun:true (drafts only, nothing written to GitHub); requires an explicit create:true to write, using sub-issue 1's resolver exclusively.
• Respects the global agent kill-switch (isGlobalAgentPause/isGlobalAgentFrozen), matching how generateContributorIssueDrafts already handles writes outside the normal dry-run chokepoint.

Deliverables

• New MCP tool definition + registration.
• Draft-generation logic parameterized by target repo and planning input (no loopover-specific signal sources baked in).
• Dedup/fingerprint-marker logic generalized to arbitrary repos.
• Create path wired exclusively to sub-issue 1's write-client resolver.

Resources

• src/services/contributor-issue-draft.ts (the pattern being generalized: draft shape, marker/fingerprint dedup, cooldown)
• src/mcp/server.ts:4212 (existing generateContributorIssueDrafts tool registration, the site for the new tool)
• src/auth/security.ts:169 (MCP_ACTUATION_REPO_ALLOWLIST, isMcpActuationRepoAllowed, requireRepoManageAccess)

Boundaries

• Draft-only default is non-negotiable per the epic's decided safety posture — no auto-create mode.
• No milestone assignment in this sub-issue; that lands in sub-issue 3, sequenced after milestone capability exists.
• Must go through sub-issue 1's resolver exclusively — no new PAT path introduced for this tool.
• Depends on sub-issue 1 landing first.

[linear-code]

JSO-5287