feat(swift-ios): support linked pull requests and GitHub sharing

[t3dotgg]

SwiftUI only read one linked pull request and could not use GitHub account sharing.

Read the full thread PR list, keep badges and search in sync, and add link and unlink actions. Open PR still opens the external URL. GitHub sharing is off by default and requires saved-endpoint permission and matching accounts on both environments.

Verified with ThreadPullRequestsTests, GitHubRoutingTests, NativeGitHubRoutingTests, and NativeThreadMetadataTests. Native CI and repository CI pass. Macroscope correctness is green, with all review findings resolved. Integrated UI evidence is handled with the main SwiftUI branch.

Created with Codex.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	13.6 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	7.0 KiB	—	7.3 KiB	✅
Codex	Live turn WebSocket wire	—	6.6 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	57.1 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	10	—	21	✅
Claude	Total thread wire	—	13.6 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	7.0 KiB	—	7.3 KiB	✅
Claude	Live turn WebSocket wire	—	6.5 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	57.8 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	9	—	21	✅

Baseline: unavailable · PR result: 750613a · 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: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

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

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR adds substantial production behavior: multi-PR thread linking plus cross-environment GitHub routing for reads and externally visible PR writes. The new wire contracts, account verification, credential-bound routing, and user-facing permission controls create a broad blast radius that requires human review.

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