fix(control-plane): isolate host completion by Goal instance

[Duang777]

Goal And Delivered Outcome

• Outcome basis / optional anchor: Reproduced control-plane settlement identity collision.
• Goal/source and gap: host_todo_completion.ts preserved an exact GoalRef in commands but derived turn_instance_id from only goal_id, agent_id, and todo_id.
• Observable before → after, with the validation row that proves it: Two Goal instances with one alias produced the same settlement identity, so the successor could be blocked by the predecessor quota receipt. Exact Goal references now use a domain-separated digest that includes goal_instance_id; alias-only requests retain their existing bytes.
• Issue/task and intended base: Self-contained bug fix against loopx-project/loopx:main.

Author Declaration

• Written by: OpenAI model agent, directed by a human operator.

Implemented against

• Specification and revision: No written specification; the request in this PR is the basis.
• Criteria:

Criterion (spec clause)	Disposition	Symbol / path	Test or command
Exact retries keep one settlement identity	implemented	turnInstanceId	host_todo_completion.test.ts
Different Goal instances cannot share a settlement identity	implemented	turnInstanceId	host_todo_completion.test.ts
Alias-only callers keep the legacy identity encoding	implemented	turnInstanceId	Existing host completion and Python adapter tests

• Self-check before submission: Reviewed the host completion, effect ID, and quota receipt call chain. Ran the focused TypeScript and Python suites, TypeScript typecheck, and diff-driven premerge. This PR does not change quota settlement schemas or Goal acceptance state.

Scope And Continuation

• Completed scope and remaining work: Complete within host Todo completion identity derivation. Goal acceptance lifetime fencing is a separate change.
• Slice boundary / successor: N/A for this defect; the fix is independently testable and preserves the alias-only contract.

Validation

• Tested revision: d06fe964a07c6e04c915c4a914888765677cacf2
• Run state: finished
• Input classes: synthetic

Check kind	Result	Public-safe evidence / limitation
unit	passed	node --no-warnings --experimental-sqlite --experimental-strip-types --test tests/control_plane_ts/host_todo_completion.test.ts: 15 passed.
integration	passed	python -m pytest -q tests/test_goal_mode_mcp_settlement.py: 8 passed.
static	passed	npm run -s typecheck:control-plane.
real_entrypoint	passed	loopx canary premerge --from-git-diff --git-diff-base upstream/main: 13 selected checks passed with no manual hold.
real_backend	not_applicable	The changed identity reducer is deterministic and does not access a provider.

• Coverage and gaps: Tests cover retry stability, cross-instance separation, downstream effect separation, and mismatched finalization. Existing adapter tests cover the alias-only path. No backend-specific path changed.

Frontend / Visual Evidence

• UI impact: none
• Before: N/A
• After: N/A
• States and viewports shown: N/A
• Source data: none
• Attention review: N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring (no functional changes)
• Documentation update
• Test update

LoopX Area

• Control plane (goals, todos, quota, scheduler, registry, runtime)
• Benchmark boundary (adapters, runners, verifiers, scoring, evidence)
• Capability or extension (providers, adapters, skills)
• Public docs or presentation surface (README, protocols, dashboard)
• Build, packaging, installer, or CI
• Host or runtime integration

Technical Direction

• Direction / acceptance reference, when applicable: Core control-plane hardening.

Shared-authority RFC fixture impact

N/A. This PR changes local identity derivation, not provider routing or shared-authority schemas.

Boundary Checklist

• Neither the diff nor this PR body/comments/attachments disclose private state, credentials, raw traces or verifier output, internal links, or local machine paths (including .loopx/, .codex/goals/, and live ACTIVE_GOAL_STATE.md).
• I did not duplicate maintainer-owned benchmark work unless a maintainer split out a public issue for it.
• I kept the change scoped to the linked issue/task.
• I completed the visual evidence section for UI changes, or marked UI impact none.
• Every commit includes a DCO Signed-off-by trailer (git commit -s).