Let a local agent hand an instruction to the Planner

Expose invoke_planner only for the full local Atomic mode. Resolve the
existing document and require a live browser login for the MCP caller's
GitHub identity; the bearer never supplies Planner ownership. Verify an
explicit checkout before posting, and retain it only for its own turn.

Persist the verbatim instruction as a member message before returning the
canonical document URL. Keep a server-opened room alive through the turn
and queue, without changing ordinary socket-only eviction. Document the
local shell and filesystem trust boundary and refusal codes.

Assistant-model: Claude Opus 5.5
Assistant-workflow: goal (run 98acf681-3730-4957-b885-0d70e0e6b32a)
Assistant-verification: bun test passed: 1718 pass, 2 PostgreSQL skips, 0 fail, 7344 assertions across 196 files
Assistant-verification: focused MCP tests passed: 87 tests, including capability gating, input bounds, output schemas, session ownership and checkout verification
Assistant-verification: harness tests passed: 141 tests; full Atomic and default isolated behavior remain covered
Assistant-verification: bun run types passed: all workspaces and E2E
Assistant-verification: bun run fix and bun run ci passed: formatting inspected; no errors, one existing lint warning and no new design findings
Assistant-verification: relative documentation links passed: 26 targets and anchors resolved with exact casing
Assistant-verification: qlty smells completed: guard-return complexity and existing archive/restore duplication recorded in implementation notes
User-preference: "Atomic's SDK is the runtime and the host supplies human input; Chopin implements HostInput rather than intercepting tools"
User-preference: "In local mode the Planner may run as a full Atomic session so workflows run inside Chopin with questions in Decisions"
Co-authored-by: Alex Lavaee <lavaman131@github.com>