feat: add the driving agent to outgoing User-Agent headers

[seancdavis]

Summary

Adds agent/<name> to the User-Agent on every request the CLI sends to a Netlify-controlled endpoint when getDrivingAgent() (#8492) detects an agent, so the API can attribute calls to agents without relying on telemetry. Also fires a telemetry event when netlify recipes ai-context installs context. Stacked on #8492.

What changed

• src/utils/user-agent.ts: one builder. getRequestUserAgent() returns USER_AGENT, plus agent/<name> when an agent is detected. It adds the name only, no version or source. The USER_AGENT text printed by --version and help is unchanged.
• src/utils/netlify-fetch.ts: netlifyFetch sets that header. The Drop API, database, logs, live tunnel, AI context, and geolocation requests use it. Log-stream websockets send the same header. The API client gets it through userAgent, and telemetry sets it directly (its header goes from netlify-cli/<version> to the full string).
• Blobs commands pass netlifyFetchForOrigin(apiURL) to @netlify/blobs, which adds the header only for the API origin. The same client also fetches presigned storage URLs, and those stay untouched, as do all third-party, presigned, and local requests.
• ai-context recipe fires sites_aiContextInstalled with { consumer }, only when it creates or updates a file. downloadAndWriteContextFiles now rejects on a failed download or write instead of swallowing it. The ticket's ai_context_installed name fails the CLI's event-name validation (it allows one underscore, and the object must be sites or user), so this uses the sites object like sites_initStarted. agent comes from EX-3042, which adds it to every event.
• Tests: every request path (API client, Drop API, telemetry, netlifyFetch, websocket) sends the same header to a local server; netlifyFetchForOrigin leaves other origins alone; the recipe tracks only real installs.

Not covered

• @netlify/config builds its own API client and ignores userAgent, so its config-resolution requests still send netlify/js-client. The same goes for @netlify/build. Fixing those needs a change in those packages.
• AI context downloads from docs.netlify.com used to send NetlifyCLI <version>; worth confirming nothing on that side parses it.

Linear: https://linear.app/netlify/issue/EX-3044/augment-cli-calls-to-identify-if-an-agent-is-performing-the-call

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• src/utils/netlify-fetch.ts

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📝 Summary

Summary by CodeRabbit

• New Features

  • Added automatic detection of supported AI coding agents, including names and versions where available.
  • Requests, including WebSocket connections, now include consistent client and detected-agent information in User-Agent metadata.
  • Blob, database, logging, geolocation, and tunnel operations now use standardized request handling.

• Bug Fixes

  • AI context telemetry is recorded only when context files are successfully written.
  • Improved request routing preserves headers for external destinations while applying Netlify metadata where appropriate.
  • AI context download failures now report errors more reliably.

Walkthrough

The change adds environment-based driving-agent detection and appends the detected agent name to request User-Agent values. Shared fetch utilities now cover API, Drop API, telemetry, service, and WebSocket requests. Drop API callers no longer provide a User-Agent. The AI context recipe reports whether files were written before recording telemetry. Tests cover detection, headers, service requests, telemetry, and recipe outcomes.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to 00d05

The change adds agent-aware request headers and more accurate AI-context telemetry without an identified merge-blocking impact.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly explains the main User-Agent changes, request coverage, origin filtering, AI context telemetry behavior, error handling, and tests. It is directly related to the changeset.
Title check	✅ Passed	The title clearly and concisely identifies the primary change: adding the detected driving agent to outgoing User-Agent headers.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 3…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Commit unit tests in branch ex-3044-agent-user-agent

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📊 Benchmark results

Comparing with 2d4360c

• Dependency count: 1,067 (no change)
• Package size: 405 MB (no change)
• Number of ts-expect-error directives: 346 (no change)

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commit: 00d059c

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Actionable comments posted: 1

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Inline comments:
In `@src/utils/netlify-fetch.ts`:
- Line 11: Remove the behavior comments at the two marked locations in the
request-routing function, preserving the existing function names, branching, and
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ℹ️ Review info

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Configuration used: Organization UI

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📥 Commits

Reviewing files that changed from the base of the PR and between 2635468 and 3862629.

📒 Files selected for processing (22)

• src/commands/blobs/blobs-delete.ts
• src/commands/blobs/blobs-get.ts
• src/commands/blobs/blobs-list.ts
• src/commands/blobs/blobs-set.ts
• src/commands/database/db-migration-pull.ts
• src/commands/database/db-status.ts
• src/commands/database/util/applied-migrations.ts
• src/commands/logs/log-api.ts
• src/lib/geo-location.ts
• src/recipes/ai-context/context.ts
• src/recipes/ai-context/index.ts
• src/recipes/blobs-migrate/index.ts
• src/utils/deploy/drop-api.ts
• src/utils/live-tunnel.ts
• src/utils/netlify-fetch.ts
• src/utils/websockets/index.ts
• tests/unit/commands/database/db-migration-pull.test.ts
• tests/unit/recipes/ai-context/download-context-files.test.ts
• tests/unit/recipes/ai-context/index.test.ts
• tests/unit/utils/live-tunnel.test.ts
• tests/unit/utils/netlify-fetch.test.ts
• tests/unit/utils/user-agent.test.ts

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• netlify/blueprints (manual)

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