chore(mobile): clear the legacy-list deletion fallout

[juliusmarminge]

The problem

Retiring the legacy grouped thread list (#13149 / #13183, both merged) left dead deletion fallout on main, flagged by an audit of the removal head:

• homeThreadList.ts still imported eight v1-only helpers and kept the recency-window constants (RECENT_THREAD_WINDOW_MS, RECENT_THREAD_FALLBACK_COUNT) only v1 read — 13 no-unused-vars warnings.
• home-list-options.ts still stored a threadSortOrder preference with a setter no screen calls; the mobile UI no longer has any thread sort order (refactor(mobile): retire the legacy grouped thread list #13183's body claimed it was gone — with this PR the claim is finally true end to end). projectSortOrder and projectGroupingMode stay; v2 uses them for scope ordering/grouping.
• homeThreadList.test.ts carried an unused threadSearchMatchKey import and NOW fixture constant; threadListV2.test.ts imported the batch availability helper it no longer calls (that coverage lives in threadOrderAvailability.test.ts).
• A HomeScreen comment still referenced "the legacy list", which no longer exists.

The fix

Also: DEFAULT_SIDEBAR_THREAD_SORT_ORDER in contracts loses its export (mobile was the last consumer of the value; the wire field keeps its internal decoding default), which is what knip flags once the mobile side is gone.

Straight deletion only — no behavior changes. The stored preference is a runtime-state field with no persisted schema; dropping it just stops a value nothing reads from being carried.

Verification: no-unused-vars clean on all touched files (HomeScreen stays at its pre-existing 13-warning baseline, unchanged), tsc --noEmit clean, full mobile suite 186 files / 1702 tests pass, formatting clean.

_{Done by Apex (Claude Opus 4.1) in pi, per the #13183 audit follow-up.}

[macroscopeapp]

Approvability

Verdict: Approved at a348da9

Macroscope's review found this PR approvable — This is a contained cleanup that removes unused mobile state, imports, constants, test fixtures, and a stale comment. The existing settings schema and updated_at decoding default remain unchanged, with no new runtime capability or meaningful behavior change.

^{You can add or adjust custom eligibility rules. Learn more.}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.5 KiB	+4 B (+0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.5 KiB	+1 B (+0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.3 KiB	56.3 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	+1 B (+0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	+1 B (+0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	0 B (0.0%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: eafb4a9 · PR result: a348da9 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 114.0 KiB
• Claude decoded thread snapshot: 114.6 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

Dismissing prior approval to re-evaluate a348da9