Define the internal forge delivery contract

docs/roadmap/implementation.md

@@ -1,6 +1,7 @@
 # Implementation plan: neutral forge delivery and credential preflight
 
-Status: ready for implementation; all stages are pending.
+Status: implementation in progress; Stage 1 is complete and Stages 2–10 are
+pending.
 
 ## Purpose and execution
 
@@ -219,7 +220,7 @@ buffering of complete binaries.
 
 ## Stage 1: Establish the internal backend contract
 
-Status: pending.
+Status: complete.
 
 1. Add `internal/forge` with the interface and logical values specified above.
    Define preflight classifications, neutral failures, and write-evidence types

internal/forge/forge.go

@@ -0,0 +1,152 @@
+// Package forge defines the backend-neutral operations used by hosted delivery.
+package forge
+
+import (
+	"context"
+	"io"
+)
+
+// Backend provides the hosted operations needed by the shared delivery
+// workflow. Implementations own destination-specific rules and protocol
+// details; the shared workflow uses only the logical values and evidence in
+// this package.
+type Backend interface {
+	// Preflight verifies credentials and access to the configured destination
+	// using read-only operations. It does not depend on a source tag or release.
+	Preflight(ctx context.Context) error
+	// TagCommit returns the commit observed for the complete tag.
+	TagCommit(ctx context.Context, tag string) (string, error)
+	// FindRelease returns the release for the complete tag. A missing release
+	// is reported with FailureNotFound.
+	FindRelease(ctx context.Context, tag string) (Release, error)
+	// CreateRelease creates the requested release and returns the protocol
+	// evidence even when an error occurs.
+	CreateRelease(ctx context.Context, request CreateReleaseRequest) (Release, WriteEvidence, error)
+	// ListAssets returns the assets attached to the release identified by handle.
+	ListAssets(ctx context.Context, releaseHandle any) ([]Asset, error)
+	// OpenAsset opens the remote asset identified by handle. The caller owns and
+	// must close the returned stream, including when reading it fails.
+	OpenAsset(ctx context.Context, assetHandle any) (io.ReadCloser, error)
+	// UploadAsset uploads content to the release identified by handle. The
+	// backend borrows content for the duration of this call and must finish any
+	// request or multipart work before returning; it must not close content.
+	UploadAsset(ctx context.Context, releaseHandle any, filename string, content io.Reader) (WriteEvidence, error)
+}
+
+// Release contains the logical release properties used by shared delivery.
+// Handle is opaque to shared code and is interpreted only by the backend that
+// produced it.
+type Release struct {
+	URL        string
+	Tag        string
+	Title      string
+	Body       string
+	Draft      bool
+	Prerelease bool
+	Handle     any
+}
+
+// CreateReleaseRequest contains the release properties requested by shared
+// delivery.
+type CreateReleaseRequest struct {
+	Tag        string
+	Commit     string
+	Title      string
+	Body       string
+	Draft      bool
+	Prerelease bool
+}
+
+// Asset contains the remote properties needed to compare an attachment with a
+// declared local asset. Handle is opaque to shared code and is interpreted only
+// by the backend that produced it.
+type Asset struct {
+	Filename string
+	Size     int64
+	Handle   any
+}
+
+// PreflightFailureKind classifies a failure to verify credentials or access to
+// a delivery destination.
+type PreflightFailureKind string
+
+const (
+	PreflightMissingCredential       PreflightFailureKind = "missing_credential"
+	PreflightInvalidCredential       PreflightFailureKind = "invalid_credential"
+	PreflightInsufficientPermissions PreflightFailureKind = "insufficient_permissions"
+	PreflightInaccessibleDestination PreflightFailureKind = "inaccessible_destination"
+	PreflightUnavailable             PreflightFailureKind = "unavailable"
+)
+
+// PreflightFailure reports a classified credential or destination access
+// failure. Err retains the underlying cause for diagnostics and cancellation
+// identity.
+type PreflightFailure struct {
+	Kind PreflightFailureKind
+	Err  error
+}
+
+func (f *PreflightFailure) Error() string {
+	if f.Err != nil {
+		return string(f.Kind) + ": " + f.Err.Error()
+	}
+	return string(f.Kind)
+}
+
+// Unwrap returns the cause of the preflight failure, if any.
+func (f *PreflightFailure) Unwrap() error { return f.Err }
+
+// FailureKind classifies a backend-neutral delivery operation failure.
+type FailureKind string
+
+const (
+	FailureInvalid      FailureKind = "invalid_request"
+	FailureNotFound     FailureKind = "not_found"
+	FailureUnauthorized FailureKind = "unauthorized"
+	FailureConflict     FailureKind = "conflict"
+	FailureMalformed    FailureKind = "malformed_response"
+	FailureUnverifiable FailureKind = "unverifiable"
+	FailureTransport    FailureKind = "transport"
+	FailureRejected     FailureKind = "rejected"
+	FailureUnknown      FailureKind = "unknown"
+)
+
+// Failure reports a backend-neutral operation failure. Backend-specific
+// status and operation details belong in Err. Err is retained for errors.Is
+// and errors.As inspection.
+type Failure struct {
+	Kind FailureKind
+	Err  error
+}
+
+func (f *Failure) Error() string {
+	if f.Err != nil {
+		return string(f.Kind) + ": " + f.Err.Error()
+	}
+	return string(f.Kind)
+}
+
+// Unwrap returns the cause of the operation failure, if any.
+func (f *Failure) Unwrap() error { return f.Err }
+
+// WriteDisposition describes the backend's evidence about a write operation.
+type WriteDisposition string
+
+const (
+	WriteNotAttempted WriteDisposition = "not_attempted"
+	WriteAccepted     WriteDisposition = "accepted"
+	WriteRejected     WriteDisposition = "rejected"
+	WriteConflict     WriteDisposition = "conflict"
+	WriteUncertain    WriteDisposition = "uncertain"
+)
+
+// WriteEvidence records whether a write was handed to the transport and what
+// its acknowledgment establishes. Accepted means the backend received and
+// decoded the required protocol acknowledgment; shared content checks still
+// apply. Uncertain means the outcome could not be established. Attempted marks
+// handoff to the transport and does not claim the server received the request.
+// Evidence remains meaningful when the operation also returns an error.
+type WriteEvidence struct {
+	Attempted   bool
+	Disposition WriteDisposition
+}