fix(shared): reject corrupted T3 Connect authorization links

[shivamhwp]

Corrupted t3 connect links currently proceed through browser authorization and fail only when the CLI receives the code. Validate the state and PKCE challenge against the canonical base64url forms generated by the CLI before starting authorization. Both loopback and headless flows use this parser.

Closes #4934. The invalid-link page now explains that the URL may be incomplete or corrupted and asks users to rerun t3 connect, then copy and open the complete fresh URL.

Validation: 24 focused shared tests pass; both corruption regressions fail before the fix. Targeted lint, formatting and diff checks pass. Internal Fable refinement remains pending.

Rebased onto main. The shared parser rejects malformed authorization values, and the web recovery message explains how to replace the link.

Model and harness: GPT-6 through Codex.

Rebased on main 20363c32c9bfdbf49c2716ef11d1f18483fcc01b. Scoped validation rerun after rebasing; existing native and human review limits remain.

Summary by CodeRabbit

• Bug Fixes
  • Improved validation of authorization requests for state and challenge values.
  • Rejects malformed values based on required base64url formatting before processing loopback port information.
  • Added coverage for corrupted authorization inputs while preserving loopback port validation.
  • Updated invalid connect-link guidance to explain that links may be invalid or corrupted and instruct users to rerun t3 connect and use the complete URL.

Follow-up validation: shared parser and web CLI-auth tests, web typecheck, scoped lint and formatting pass. The text-only recovery copy has not had a new browser screenshot pass.

Browser evidence

The actual Connect authorization component was rendered in Chromium with the same synthetic URL containing a terminal border character in state. Baseline calls Clerk sign-in once; head 7def49addd0d17754f416d7b602d0ff96e036088 rejects it with recovery guidance and never calls sign-in. A valid request on the patched component still calls sign-in once.

Before	After

This is a browser component reproduction with the production parser, component and styles. Clerk hooks are stubbed to observe calls without authorizing an account. Hosted route bootstrapping, real Clerk sign-in, and browser-to-CLI code exchange were not exercised. Screenshot labels disclose the fixture.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — The PR is a narrow, well-tested fix that rejects malformed OAuth state and PKCE challenge values before authorization. Because it changes authentication-link validation and the authorization flow, human review is required despite the limited diff.

No code changes detected at 7def49a. Prior analysis still applies.

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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	13.5 KiB	13.6 KiB	+50 B (+0.4%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	−3 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.6 KiB	+53 B (+0.8%)	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	−63 B (−0.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	−5 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.5 KiB	−58 B (−0.9%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.9 KiB	57.8 KiB	−88 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	8	−2 (−20.0%)	21	✅

Baseline: e628683 · PR result: 7def49a · 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.

[greatitself]

Independent validation of 4e60b590364e1c40417155de61a4b8e59b85b0f3 (merge-base 050e2cafb144).

Exercised the unused base64url bits systematically: 256 valid state/challenge pairs all round-tripped. For each pair, changed only unused bits in the final character: 15 state variants and 3 challenge variants. This revision rejected all 4,608 noncanonical variants; the merge-base accepted them. This is URL-parser validation, not an end-to-end authorization test.

Reproduction scripts and recorded results — first.mjs; the numbered metadata file pins this PR’s tested revisions.

Model: GPT-6. Harness: Codex.

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• apps/web/src/components/cloud/ConnectCliAuthSurface.tsx

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📝 Walkthrough

Walkthrough

readConnectAuthorizeRequest now rejects malformed state and PKCE challenge values before authorization processing. Tests cover invalid encodings and valid loopback authorization cases. The connect surface updates its invalid-link guidance.

Changes

Connect authorization validation

Layer / File(s)	Summary
Strict state and challenge validation packages/shared/src/connectAuth.ts, packages/shared/src/connectAuth.test.ts	readConnectAuthorizeRequest validates base64url lengths, characters, and unused-bit patterns for state and challenge. Tests cover malformed values and valid loopback fixtures.
Invalid connect-link guidance apps/web/src/components/cloud/ConnectCliAuthSurface.tsx	The invalid-link message identifies invalid or corrupted links and instructs users to rerun t3 connect and use the complete URL.

Priority: ➖ Normal

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

Change: Bug fix · Severity of issue fixed: Low

Merge Risk: ⚪ Minimal · up to 7def4

The change rejects corrupted authorization links before sign-in and provides clear recovery instructions without introducing an identified merge-blocking risk.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description explains what changed, why it changed, the UI impact, validation, browser evidence, and limitations. It does not reproduce the template headings or checklist, but it provides the requi…
Linked Issues check	✅ Passed	The description closes issue #4934, and the stated changes directly address that issue by rejecting malformed authorization values before authorization begins.
Out of Scope Changes check	✅ Passed	The changes remain focused on the parser, corruption regression tests, and the related invalid-link recovery message. These changes match the stated objectives.
Title check	✅ Passed	The title clearly and concisely describes the main change: rejecting corrupted T3 Connect authorization links.

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Actionable comments posted: 1

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Inline comments:
In `@packages/shared/src/connectAuth.ts`:
- Around line 65-75: Update the `/connect` invalid-link message used for
malformed state or PKCE challenge values to mention that the URL may be
corrupted and instruct users to copy the freshly printed URL again, while
preserving the existing guidance to rerun `t3 connect` and open the new URL.

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• packages/shared/src/connectAuth.test.ts
• packages/shared/src/connectAuth.ts

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[juliusmarminge]

Superseded by #11794, which replaced the headless connect paste/callback flow with Clerk's device authorization grant and closed #4934. Closing this PR as leftover hygiene.