fix: prepare MCP tools for marketplace submission

[skvark]

Summary

• require readOnlyHint, openWorldHint, and destructiveHint on every shared MCP tool descriptor
• classify bounded service-side effects using observable public behavior
• advertise text-v1 as the explicit default and first enum value for every format-selectable MCP tool
• add concise text-over-JSON guidance to the MCP skills, server instructions, and installed agent guidance
• retain JSON as an opt-in compatibility mode without duplicating large payloads into structuredContent
• add full-surface regression coverage and public reviewer justifications

Release

• githits: 0.6.3 → 0.6.4
• @githits/mcp: 0.6.2 → 0.6.3
• align the root package, plugin manifests, Gemini extension, and MCP registry package entry at 0.6.4
• publish both packages through their existing merge-triggered workflows

Why

OpenAI marketplace validation rejects the remote MCP because several tools omit required impact annotations. The remote server consumes tool semantics from @githits/mcp, so the fix belongs in the shared package.

Some tools may create bounded service-side state or begin background preparation when requested public content is not immediately available. The annotations reflect that maximum observable impact without exposing implementation details or implying public, external, or destructive writes.

A published user trace also showed an agent explicitly selecting JSON in 86 of 91 calls despite GitHits' compact text default. The input schemas previously listed json first and did not encode a JSON Schema default. They now expose default: "text-v1" with enum order text-v1, text, json.

Output schema decision

outputSchema is intentionally deferred. The current tools return MCP TextContent, not structuredContent; MCP makes outputSchema optional and requires successful structured results to conform when one is declared. Mirroring the existing JSON envelopes into structuredContent would make default calls carry both compact text and the full structured payload, increasing context use for code, search results, documentation, changelogs, and dependency graphs.

A future structured contract should contain only compact control-plane fields such as status, IDs, cursors, counts, truncation, and next actions—not duplicate large result bodies.

Impact

The MCP schema now always exposes explicit boolean values for all three marketplace impact hints. Tool response behavior and explicit JSON compatibility are unchanged; model-facing schemas and guidance now make the token-efficient format default unambiguous.

Validation

• bun test — 2,483 passed
• bun run typecheck
• bun run build
• bun run validate:packages
• bun run validate:packages:mcp-publish
• full source MCP smoke, including default text and explicit JSON calls
• source and built MCP registration smoke tests
• source and built unauthenticated CLI smoke tests
• mcp-publisher v1.7.9 validation against the official registry
• canonical MCP skill validation
• targeted Biome checks for changed files
• Claude package-information agent eval: 2 relevant calls, neither sent format, no tool or instruction issues

The optional authenticated CLI live smoke reached its final example request and received a backend 429; the secret-free CLI modes passed.