Migrate to new Stacks REST API

[skarim]

With the upcoming release of the public REST API for stacked pull requests (/repos/{owner}/{repo}/stacks), this will replace the temporary cli_internal endpoints that gh-stack had previously been using. This moves every stack operation onto it. Because the API is public, it also lifts the auth restriction added in #113: anyone authenticated with the GitHub CLI can run stack operations once the feature is enabled for their repo — the OAuth-only limitation is gone.

What the new API gives us

• List (GET /stacks) with a server-side ?pull_request=N filter to find the stack a PR belongs to.
• Detail (GET /stacks/{number}) — fetch a single stack by its number.
• Create (POST /stacks) — returns the created stack, including its number.
• Add (POST /stacks/{number}/add) — append PRs to the top of a stack (delta only; we no longer resend the full PR list).
• Unstack (POST /stacks/{number}/unstack) — the server decides which PRs can be removed.

Behavior changes worth noting

• Discovery uses the ?pull_request= filter instead of listing every stack and scanning client-side.
• Updates are append-only. There is no full-replace endpoint, so submit and link compute the delta and append it. A desired change that isn't a clean append onto the remote stack — a reorder, or a removal such as merged PRs leaving the stack — is left untouched rather than force-rewritten.
• unstack is now server-driven. The old client-side eligibility pre-check is gone. The server removes the unlocked PRs and returns 204 when the stack is fully dissolved, 200 when some PRs (queued for merge or with auto-merge enabled) remain, or 422 when nothing can be removed. unstack keeps local tracking when PRs remain on the stack.

Changes

Add stack Number field to local model and schema

• internal/stack/stack.go, schema.json — add the Number field to the Stack model and document it. Additive only; nothing populates it yet.

Cut over stack operations to the public Stacks REST API

• internal/github/github.go — the core of the change. Point the client at the new /stacks endpoints and rework RemoteStack to carry the stack's id, number, base, open state, and PR list. Adds FindStackForPR (the ?pull_request= lookup), GetStack, AddToStack (delta append), and a Unstack that distinguishes the 204 (dissolved) from 200 (PRs remain) responses. client_interface.go and mock_client.go follow the new method set.
• cmd/submit.go, cmd/link.go — reconcile against the remote stack via the ?pull_request= lookup and express updates as delta appends rather than resending the full list.
• cmd/checkout.go — discover a PR's stack through FindStackForPR instead of scanning every stack.
• cmd/unstack.go — drop the client-side eligibility pre-check and react to the server's 204/200/422 result, keeping local tracking when PRs remain.
• cmd/utils.go — shared helpers for the sync reconcile path and for resolving a stack's number from its id.
• cmd/*_test.go — command tests updated for the new client surface and mock.

Remove the personal access token (PAT) limitation

• Delete internal/config/auth.go and auth_test.go, and the TokenForHostFn test hook in config.go.
• cmd/submit.go drops the PAT pre-flight; cmd/utils.go renames warnStacksUnavailableOrPAT → warnStacksUnavailable, and checkout.go / link.go drop the PAT-specific messaging. A 404 now simply means stacked PRs aren't enabled for the repo.

Testing

• Updated the affected command tests for the new client surface and the server-driven unstack semantics.
• Verified the create → add → unstack round-trip against the live API on a test repo, including the delta-append and 204/200/422 paths.
• go test -race ./..., go vet ./..., and gofmt are clean, and each of the three commits builds and passes tests independently.

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_{Stack created with GitHub Stacks CLI • Give Feedback 💬}

[Copilot]

Pull request overview

Migrates stack operations from temporary internal endpoints to the public Stacks REST API.

Changes:

• Adds stack numbers and public REST API client methods.
• Updates submit, link, checkout, sync, and unstack workflows.
• Removes PAT-specific restrictions and updates tests.

Show a summary per file

File	Description
internal/stack/stack.go	Adds stack number storage.
internal/stack/stack_test.go	Tests number persistence.
internal/stack/schema.json	Documents the number field.
internal/github/mock_client.go	Updates stack API mocks.
internal/github/github.go	Implements public REST stack operations.
internal/github/client_interface.go	Updates the client interface.
internal/config/config.go	Removes the token test hook.
internal/config/auth.go	Removes PAT detection.
internal/config/auth_test.go	Removes PAT tests.
cmd/utils.go	Adds number resolution and reconciliation support.
cmd/utils_test.go	Updates warning tests.
cmd/unstack.go	Adopts server-driven unstacking.
cmd/unstack_test.go	Tests new unstack semantics.
cmd/sync_test.go	Updates sync API mocks and expectations.
cmd/submit.go	Implements append-only stack reconciliation.
cmd/submit_test.go	Updates submit and modify-recovery tests.
cmd/link.go	Uses delta-based stack additions.
cmd/link_test.go	Tests additive linking behavior.
cmd/checkout.go	Uses filtered discovery and stack numbers.
cmd/checkout_test.go	Updates remote checkout tests.

Review details

• Files reviewed: 20/20 changed files
• Comments generated: 7
• Review effort level: Medium

[talum]

👍🏼