fix(client): load earlier turns works for MCP threads over T3 Connect

[juliusmarminge]

Over T3 Connect, "Load earlier turns" on a thread created through MCP tools (id mcp:…) failed with "The environment rejected this client's credentials (invalid_credential)." The server log showed environment.dpop.failure_code: "url_mismatch".

The DPoP proof signed /api/orchestration/threads/mcp:…/history with the raw id, while the HttpApi client sent the percent-encoded path /threads/mcp%3A…/history. The environment compares the proof against the URL it received, so it rejected the request. The credential refresh-and-retry signed the same wrong URL, so it failed too. Thread snapshot and bounded snapshot requests built their URLs the same way.

The fix encodes the thread id in all three signed URLs. A new test loads each one with an mcp: id and checks that the signed URL equals the URL actually fetched. Without the fix the test fails.

Possible follow-up: the signed URL and the sent URL are still built separately. Signing the request URL the client actually sends would rule out this whole class of bug.

Done by Claude Opus 5.5 in Claude Code (via T3 Code).

🤖 Generated with Claude Code

Fixes #15772

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[macroscopeapp]

Approvability

Verdict: Approved at 231683b

Macroscope's review found this PR approvable — This is a focused client bug fix that aligns DPoP-signed URLs with the percent-encoded URLs actually sent for MCP thread IDs. It touches only three existing request paths and adds targeted regression coverage for all of them.

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[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 454b94a and 231683b.

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📒 Files selected for processing (4)

• packages/client-runtime/src/state/boundedThreadSnapshotHttp.ts
• packages/client-runtime/src/state/environmentHttpAuth.test.ts
• packages/client-runtime/src/state/threadHistoryHttp.ts
• packages/client-runtime/src/state/threadSnapshotHttp.ts

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📝 Walkthrough

Walkthrough

Snapshot, bounded snapshot, and history request paths now percent-encode thread IDs. Added tests use an ID containing a colon and verify the encoded request path and DPoP proof URL.

Changes

Thread ID path encoding

Layer / File(s)	Summary
Encode thread IDs in request paths packages/client-runtime/src/state/threadSnapshotHttp.ts, packages/client-runtime/src/state/boundedThreadSnapshotHttp.ts, packages/client-runtime/src/state/threadHistoryHttp.ts, packages/client-runtime/src/state/environmentHttpAuth.test.ts	Snapshot, bounded snapshot, and history request paths encode thread IDs before URL interpolation. Tests check encoded paths and confirm that the DPoP proof URL matches the sent URL without its query string.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

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Merge Risk: ⚪ Minimal · up to 23168

No actionable issue is established for the reported MCP thread-ID fix. The change is mergeable after normal checks.

Pre-merge checks | 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly identifies the fix for loading earlier turns in MCP threads over T3 Connect.
Description check		The description explains the problem, the URL-encoding change, and the added test. It links issue #15772, but does not state that the issue is triaged or include maintainer approval. It also does not …

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[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	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.9 KiB	20.9 KiB	0 B (0.0%)	29.3 KiB	✅
Codex	Live turn messages	2	2	0 (0.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.2 KiB	21.2 KiB	0 B (0.0%)	29.3 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: 454b94a · PR result: 231683b · 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: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

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