test: characterize set_widget LWW gate

[christian-byrne]

Summary

• Add permanent characterization coverage for the top-level set_widget LWW gate.
• Verify lower keys are dropped, higher keys and first writes apply, and equal counter/actor keys resolve by op_id.

Contract corrections

The queue row expected two behaviors that the protocol does not provide:

1. A different op_id cannot produce an equal full stamp key. Ordering is [counter, actor, op_id], so this test covers the real tie case: equal counter and actor, resolved by op_id.
2. lww-dropped consumes the losing op_id in __applied. Therefore the contested widget value and stamp remain unchanged, but the full Yjs document encoding changes due to bookkeeping.

No production behavior or outcome strings change.

Invariants

• KA-2: ordering and identity travel inside the operation.
• KA-4: deterministic, idempotent application.
• FC-7: retry identity preserves op_id and conflict ordering uses stamps.

Verification

• npm test -- test/set-widget-lww-gate.test.ts — 4 passed
• npm test — 69 files, 855 passed
• npm run typecheck — passed
• npm run lint — 0 errors (1491 existing warnings)
• required repository checks and corpus verification — passed

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📥 Commits

Reviewing files that changed from the base of the PR and between 52d659b and 5088a5a.

📒 Files selected for processing (1)

• test/set-widget-lww-gate.test.ts

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[benceruleanlu]

Approved.

Review findings

suggestion: In test/set-widget-lww-gate.test.ts, the op_id tiebreak case applies the higher ID before the lower one, so this file remains green if the top-level gate compares only the counter. The broader suite already kills that mutation across the LWW, KA-2, convergence, replay, and property coverage, so this is not a repository safety gap. For stronger standalone characterization, consider adding the reverse op_id arrival order and an equal-counter/different-actor case (KA-2, FC-2, FC-7).

[christian-byrne]

Follow-up PR addressing the review item: #176 (assigned to christian-byrne per quiet-week contact rules; approver named in the PR body).

Full context for agent readers

Both requested cases landed in test/set-widget-lww-gate.test.ts: the reverse op_id arrival order (lower first, higher must apply) and an equal-counter/different-actor case in both arrival orders. Mutation check recorded in the PR body: under a counter-only gate the original 4 tests stay green and both new tests fail, so the file now kills that mutation standalone. Focused 6/6 green; typecheck and lint clean; the 8 check-import-graph.test.ts failures in the full run reproduce on pristine main and are unrelated. Filed by fleet lane lane-act-cmp-161-followup-1709 for row act-cmp-161-followup.