fix(dispatcher): Verify installer attestation before running self-update

[hatayama]

Summary

The dispatcher self-update flow (uloop update and the scheduled 24h refresh) now requires a valid Sigstore attestation for install.sh / install.ps1 before executing the downloaded installer.

This is Phase B2 of TODO 2 (docs/spec — 2026-07-09 uloop CLIインストールのセキュリティ改善). Phase B1 (verifier package, PR #1670) is already merged; Phase B3 will wire the same verifier into the project runner download path.

User Impact

Before: A compromised GitHub releases origin could serve a malicious install.sh + matching install.sh.sha256, and the dispatcher would happily execute it — sha256 alone cannot prove authenticity when the checksum ships from the same origin as the asset.

After: The installer will not run unless the bundled .sigstore.json cryptographically verifies against Sigstore's public-good trust anchor, the workflow identity matches .github/workflows/dispatcher-publish.yml on an allowed ref (refs/heads/v3-beta or refs/heads/main), and the release tag's commit SHA matches the certificate's Source Repository Digest extension. Fail-closed on bundle-missing, network-failure, digest-mismatch, and identity-mismatch.

Changes

• update.Command gains a ReleaseTag field so the verifier can resolve the tag to a commit SHA for OID 1.3.6.1.4.1.57264.1.13 binding.
• attestation_verify.go wires the internal/attestation package into the dispatcher package with a swappable var (verifyReleaseAssetAttestation) so unit tests can isolate download/checksum logic from real Sigstore verification. Exposes both publish-workflow SANs (dispatcher-publish, native-cli-publish) so Phase B3 can reuse the constants.
• downloadVerifiedUpdateInstaller calls the verifier with attestationDispatcherPublishWorkflowPath after the sha256 check succeeds.
• Existing tests updated to stub the attestation hook (unchanged behavior). New tests cover fail-closed on attestation error and the exact release-tag / workflow-path passed to the hook.

Verification

• scripts/check-go-cli.sh — 0 lint issues across all Go modules
• go test ./... in cli/dispatcher/ — all packages pass, including attestation + dispatcher

Refs: docs/plans/ spec, TODO 2 Phase B2

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Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 7088d4a and 16d5b78.

📒 Files selected for processing (5)

• cli/dispatcher/internal/dispatcher/attestation_verify.go
• cli/dispatcher/internal/dispatcher/attestation_verify_test.go
• cli/dispatcher/internal/dispatcher/update.go
• cli/dispatcher/internal/dispatcher/update_test.go
• cli/dispatcher/internal/update/command.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/attestation-integrate-update

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