feat(auth): add the device grant protocol state machine

[Chase J (chajac)]

Note

First of five stacked PRs that add browser sign-in with the WorkOS device flow. Order: this one, then #1570, #1571, #1572, #1573. Each targets the branch below it. #1564 and #1565 hold the earlier single-branch version, with its review history.

Overview of Problem

qawolf auth login has one path: paste an API key. Browser sign-in needs the OAuth device authorization grant, which has protocol decisions worth testing without a clock or a socket: polling intervals, slow_down, terminal error codes, the deadline, and connection backoff.

This PR adds only pure code. Nothing calls it yet.

Where to look

File	Why
core/deviceAuth/pollState.ts	Every protocol decision, as a pure function. pollState.test.ts reads as the specification.
core/deviceAuth/tokenExpiry.ts	Reads the exp claim from the access token, which is the only expiry the token response carries.

Overview of Changes

• core/deviceAuth/types.ts names the token pair, the poll responses, and the poll state.
• core/deviceAuth/pollState.ts decides what a poller does next. Tokens win over the deadline, slow_down raises the interval for the rest of the flow, and a dropped connection doubles it.
• core/deviceAuth/tokenExpiry.ts decodes the expiry without verifying the signature. The value decides when to refresh; the API judges whether a token is genuine.

Testing

• 21 new tests. oxlint --max-warnings 0, oxfmt --check, tsc --noEmit and knip are clean.

To Do

• Request e2e test coverage if needed
• Explain database migrations and whether they have been manually written or auto-generated — none
• Add release notes in sections below if your changes are relevant to non-developers — none, no user-visible change
• Add pre/post-release tasks in sections below if needed

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📥 Commits

Reviewing files that changed from the base of the PR and between 923dfb8 and d28a2a7.

📒 Files selected for processing (4)

• src/core/deviceAuth/pollState.test.ts
• src/core/deviceAuth/pollState.ts
• src/core/deviceAuth/tokenExpiry.test.ts
• src/core/deviceAuth/tokenExpiry.ts

Walkthrough

Added device authorization contracts for tokens, polling responses, polling state, and polling outcomes. Added readAccessTokenExpiry to decode JWT payloads and convert valid exp claims to milliseconds. Added nextPollStep to handle completion, pending polling, interval backoff, timeout, denial, expiration, and network errors. Added tests for token expiry parsing and polling transitions.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🔵 Low · up to 923df

The new device-auth token expiry helper can return an invalid infinite expiry for an extreme token claim, which could interfere with expiry handling when consumed. Add a finite-result check before merge.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title follows Conventional Commits with the valid feat(auth) prefix. It uses imperative wording, clearly describes the device grant state machine, stays under 72 characters, and has no trailing …
Description check	✅ Passed	The description explains the problem, scope, implementation areas, and testing results. It includes Overview and Testing content, but it does not include the template's Checklist section and does not …

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• Create PR with unit tests
• Commit unit tests in branch connect-core

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Actionable comments posted: 1

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Inline comments:
In `@src/core/deviceAuth/tokenExpiry.ts`:
- Line 29: Update the expiry conversion in the token-expiry logic so that after
multiplying finite exp by 1,000, non-finite results return undefined instead of
an infinite epoch-millisecond value. Add a test covering multiplication overflow
and preserve the existing conversion for valid finite results.

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• src/core/deviceAuth/pollState.test.ts
• src/core/deviceAuth/tokenExpiry.ts
• src/core/deviceAuth/types.ts

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