Type granular issue MCP inputs and protocol-gated outputs

[SamMorrowDrums]

Summary

Migrate all 16 remaining granular issue tools to concrete typed input/output registrations, preserving legacy text and exposing output schemas/structured content only for protocol 2026-07-28. Keep the already-typed hide/unhide tools unchanged.

Why

Continue the protocol-gated typed-tool migration above #3393, pinned to parent c3f5817fe2c0f87b778e0a9bc53af887059e72d3.
Fixes # N/A — stacked migration, not an issue closure.

What changed

• Type create, single-field updates, custom fields, sub-issue mutations, and issue/comment reaction tools; retain input schemas, numeric coercions, confidence normalization, validation/errors, scopes and feature rules.
• Reuse typed parent/sub-issue helpers, preserve nullable custom-field scalar outputs and exact API payloads, and add modern/legacy/unknown wire contracts plus schema snapshots.

MCP impact

• No tool or API changes
• Tool schema or behavior changed — modern clients receive concrete output schemas and structured content; legacy/unknown clients retain exact text without either. Existing input schemas remain unchanged.
• New tool added

Prompts tested (tool changes only)

• Automated MCP wire equivalents, not live natural-language sessions: create an issue under a cross-repository parent; update assignees/labels/type/state with suggestion metadata; set each custom field type; add/remove/reprioritize sub-issues; add/remove every supported issue/comment reaction; hide/unhide an issue comment.

Security / limits

• No security or limits impact — no new endpoints or permissions.
• Auth / permissions considered — repo scope, granular feature flags, read-only visibility and existing error handling retained and covered.
• Data exposure, filtering, or token/size limits considered — reuse existing sub-issue sanitization; protocol-gated structured content mirrors legacy results.

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

• Linted locally with ./script/lint — script/lint passed, 0 issues.
• Tested locally with ./script/test — script/test passed, full race suite.

Additional validation: UPDATE_TOOLSNAPS=true go test ./... passed; script/generate-docs passed with no documentation delta; git diff --check passed. Live PAT-backed e2e tests were not run. Signed coauthored commit 83955ca85c929687a0630503dcc061b1b9af4537.

Docs

• Not needed — documentation generator completed; published inputs/tool descriptions did not change.
• Updated (README / docs / examples)

Keep this PR draft. Stack metadata is intentionally untouched; the coordinator will append after verification.