feat(fetchsvc): in-sandbox fetch-skill subcommand (Phase 4, PR 2)

[ggallen]

Summary

• Adds fullsend fetch-skill <url> subcommand for agents to fetch skills at runtime from inside the sandbox, communicating with the runner-side fetch service over HTTP with bearer token auth
• Adds fetch server lifecycle management (startFetchService) with dynamic TCP port allocation, per-run UUID bearer token (timing-safe comparison), and graceful shutdown
• Adds SandboxUploader adapter wrapping sandbox.UploadDir to implement the fetchsvc.Uploader interface
• Wires the fetch service into runAgent() and injects FULLSEND_FETCH_URL / FULLSEND_FETCH_TOKEN env vars during sandbox bootstrap
• Includes carryover fixes from feat(fetchsvc): runner-side runtime fetch service (Phase 4, PR 1) #2173 review: CachePutDir return value correctness, audit log error propagation, MaxBytesError → 413

Context

This is Phase 4, PR 2 of ADR-0038 (Universal Harness Access). PR 1 (#2173) delivered the runner-side fetchsvc package. This PR completes the client side so agents can invoke fullsend fetch-skill inside the sandbox. PR 3 will add allow_runtime_fetch / max_runtime_fetches harness schema fields to gate the feature.

Key decisions

• Subcommand, not separate binary — reuses the fullsend binary already uploaded to /sandbox/workspace/bin/fullsend, avoiding cross-compilation and GoReleaser changes
• HTTP over TCP, not Unix socket — OpenShell sandboxes are containers with no shared filesystem; TCP through the L7 proxy is the established transport (ADR-0046)
• Bearer token auth — per ADR-0046, a per-run random token delivered via env var; timing-safe comparison prevents timing attacks

Test plan

• 10 unit tests for fetch-skill subcommand (success, error codes, missing env, auth propagation, request body, timeout)
• 7 unit tests for fetch server (lifecycle, fetch endpoint, auth rejection, token validation, token generation)
• go test ./... — all 28 packages pass
• go vet clean
• make lint passes
• fullsend fetch-skill --help displays correct usage

🤖 Generated with Claude Code

[github-actions]

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Commit: 6f269dbfd59255ec730129069c1d71a2ae70d1dc

[fullsend-ai-review]

🤖 Finished Review · ✅ Success · Started 12:54 PM UTC · Completed 1:07 PM UTC
Commit: 6f269db · View workflow run →

[fullsend-ai-review]

Review skipped — this PR is already closed.

The /fs-review command only reviews open pull requests.

_{Posted by fullsend pre-review check}

[codecov]

Codecov Report

❌ Patch coverage is 56.39098% with 58 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/cli/run.go	0.00%	28 Missing ⚠️
internal/cli/fetchskill.go	67.92%	11 Missing and 6 partials ⚠️
internal/cli/fetchserver.go	79.48%	4 Missing and 4 partials ⚠️
internal/fetchsvc/service.go	70.00%	1 Missing and 2 partials ⚠️
internal/fetchsvc/uploader.go	0.00%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

[fullsend-ai-retro]

🤖 Finished Retro · ✅ Success · Started 12:58 PM UTC · Completed 1:04 PM UTC
Commit: 6f269db · View workflow run →

[fullsend-ai-retro]

Retro: PR #2221 — closed-and-replaced PR triggered wasted agent runs

What happened: PR #2221 (feat(fetchsvc): in-sandbox fetch-skill subcommand) was opened by ggallen at 12:51 UTC and closed 3 minutes later at 12:54 UTC without merge. The author deleted the branch and immediately re-created the PR as #2223 at 12:54 UTC. During those 3 minutes, the review agent was dispatched (run 27416794686) but the PR was closed before review completed, so the review bot posted "Review skipped — this PR is already closed." A retro dispatch was also triggered on the closed PR.

Wasted work: The review run consumed tokens and compute before discovering the PR was closed. The retro run (this one) was also dispatched unnecessarily on a PR with no agent interaction and no merge.

No new proposals — all improvements already tracked:

Improvement	Existing issues
Skip review/fix dispatch when PR is closed	#1870, #1439
Check PR state before posting review results	#885
Skip retro for closed-without-merge PRs with immediate successor	#2176, #1411
Cancel in-progress review dispatches on same PR	#1357

This PR is a textbook case for all of these issues. Prioritizing #1870 and #2176 would prevent the most common source of wasted agent runs in close-and-recreate workflows.

[fullsend-ai-review]

Review skipped — this PR is already closed.

The /fs-review command only reviews open pull requests.

_{Posted by fullsend post-review check}