Converge client error surfaces to the ruled C5 per-operation leaf-error shape

[coenttb]

Problem. This package's live typed clients use a whole-client generic Failure parameter (@Sendable (Request) async throws(Failure) -> Page, traversal errors like Traversal.Error<Failure>). The ruled target shape for client families (principal, 2026-07-31; C5 step-0 ruling swift-foundations/swift-witnesses#3 comment 5143970225) is per-operation domain-specific leaf errors via Either<Async.Lifecycle.Error, Leaf> — whole-client Client<Failure> genericism was explicitly rejected. swift-standards/swift-stripe-standard realized the ruled shape at fd63cd0 (309 operations, run 30698829457) and is the exemplar.

Proposed outcome. This package's client surfaces converge to the C5 shape: per-operation leaf enums at noun namespaces, Either<Async.Lifecycle.Error, Leaf> throws, Never for infallible operations, with the traversal-composition design mapped onto leaf errors rather than a generic parameter (the exact traversal mapping is a design element for the external-API first-principles programme — record the chosen mapping here before mass execution). Sequenced within the ruled migration order (after mailgun's vehicle; before identities-types closes the arc).

[coenttb]

API ruling (principal, 2026-08-02)

GitHub traversal operations shall throw Either<Async.Lifecycle.Error, Traversal.Error>; Traversal.Error is non-generic, owns only traversal invariants plus case page(Page.Error) for the invoked operation’s domain leaf, and no lifecycle or generic client failure cases.

This applies the C5 lifecycle/leaf separation recorded in swift-witnesses #3. It is the governing mapping for this task and the serialized resource-target decomposition in #7.

[coenttb]

Page-error taxonomy ruling (2026-08-02).

This completes the public leaf-error decision required by the approved outer C5 ruling in the prior API ruling.

The three traversal-backed page operations use resource-level namespaces, not Client.Page:

• GitHub.Organization.Repositories.Page
• GitHub.Repository.Stargazers.Page
• GitHub.User.Repositories.Page

Each Client is non-generic and injects @Sendable (Request) async throws(Either<Async.Lifecycle.Error, Page.Error>) -> Page.

The exact non-generic, payload-free page leaves are:

• organization repositories: transport, malformedResponse;
• repository stargazers: transport, rejected, malformedResponse;
• authenticated-user repositories: transport, authentication, forbidden, rejected, malformedResponse.

The leaf enums are non-@frozen and conform to Swift.Error, Sendable, Equatable, and Hashable. None is Never. rejected represents documented HTTP 422 validation-or-spam rejection without inventing a typed response payload; 304 is omitted because these requests expose no conditional validator.

Traversal.Error remains non-generic and retains only traversal invariants plus case page(Page.Error). Page lifecycle failures pass through on Either.left; page leaves map to Either.right(.page(error)); traversal invariants remain Either.right. Remove former cancellation and client(Failure) cases. Adapter details—HTTP status, request construction, JSON/pagination parsing, and execution errors—map to these leaves and never enter L3 as GitHub.HTTP.Error, HTTP.Status, parser errors, any Error, or generic placeholders.

This applies the lifecycle/leaf rule in swift-witnesses #3 and reuses Async.Lifecycle.Error / Either; the three operation-specific page enums are implemented once in this L3 owner.

[coenttb]

Implementation receipt — non-closing; Task #6 remains OPEN and assigned.

PR: #9 at 6b038679108f76d156417c89280e7521ecec9991 (base 7ce3cbd10f6bf1afe1433cccb41e2de6d6531be6).

Applied the C5 page-error taxonomy ruling: resource Page namespaces, non-generic page clients, and Either<Async.Lifecycle.Error, Traversal.Error> traversal operations. Traversal.Error now holds traversal invariants plus page(Page.Error) only; lifecycle failures remain the left arm. Composition: direct Async Lifecycle Primitives and Either Primitives dependencies/imports; no target or product split.

Verification: workspace package test --package-path . --fresh --jobs 4 passed (17 tests); workspace package lint --package-path . exited 0 with 38 pre-existing advisory findings. #7 is now unblocked to perform its separately serialized target/product decomposition after this PR lands.

[coenttb]

HOLD — PR #9 remains independently source-reviewed at exact head 0f49fa7.

Qualifying full-tier workflow_dispatch run https://github.com/swift-foundations/swift-github/actions/runs/30745670726 is non-terminal: 16 of 20 jobs are complete, and the remaining four are queued exclusively for macos-26 hosted runners. The bounded queue diagnosis confirmed that Actions is enabled, the dispatch is valid and has executed jobs, and no same-repository workflow run is in progress. The run-level conclusion is not yet available.

Recheck trigger: run 30745670726 reaches a terminal state. At that point, adjudicate the run-level conclusion; merge PR #9 and close Task #6 only if it succeeds.

Task #6 is being unassigned because no source, review, or CI action remains actively in flight.