refactor(shared): remove unused runtime helpers and exports

[juliusmarminge]

Shared exports several implementation helpers that no consumer uses.

Remove the four unused model, composer, and source-control helpers and keep remaining implementation-only functions/constants private. Preserve exported types and Effect schemas under the revised Knip policy. Keep the public Net constructor required by the repository's Effect service convention.

Verification: shared typecheck and existing shared/source-control tests pass on the rebased stack. The integrated Knip gate passes. No existing tests were changed or removed.

Model: gpt-6 astra. Harness: Codex in T3 Code.

[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	13.6 KiB	+71 B (+0.5%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	+6 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.6 KiB	+65 B (+1.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	57.1 KiB	+88 B (+0.2%)	66.4 KiB	✅
Codex	Live turn messages	8	10	+2 (+25.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.6 KiB	−3 B (−0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	−8 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	+5 B (+0.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.8 KiB	57.8 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: cb9a694 · PR result: 56a7d66 · 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: 113.8 KiB
• Claude decoded thread snapshot: 114.5 KiB

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

[macroscopeapp]

Approvability

Verdict: Approved at 56a7d66

Macroscope's review found this PR approvable — This is a contained shared-code cleanup that narrows unused exports and keeps all internally used implementations and values unchanged. No new capability, product-default change, deployment change, or sensitive-area modification is introduced.

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Dismissing prior approval to re-evaluate b74ac25

[cursor]

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Dismissing prior approval to re-evaluate d5f8565