feat(e2e): MSW cassette layer for hermetic e2e tests#1920
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Stephen Belanger (Qard) merged 22 commits intomainfrom May 6, 2026
Merged
feat(e2e): MSW cassette layer for hermetic e2e tests#1920Stephen Belanger (Qard) merged 22 commits intomainfrom
Stephen Belanger (Qard) merged 22 commits intomainfrom
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Vendors the seinfeld VCR/cassette library into the monorepo under dev-packages/seinfeld. The package wraps MSW to record and replay HTTP traffic in tests — record mode hits real providers and writes JSON cassette files; replay mode intercepts fetch and serves the recorded responses deterministically. Key features: - Two-pipeline design: normalizers (matching-only) vs redactors (persistence) - Built-in filter presets strip volatile headers/params before matching - Paranoid redaction preset masks auth headers and credential-shaped body fields - Vitest integration (setupCassettes) for per-test cassette lifecycle - passthroughHosts option to exempt specific hosts from interception Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Removes e2e/helpers/cassette/ and the parent-process recorder server.
Replaces them with @braintrust/seinfeld, the workspace package added in
the preceding commit.
Key changes:
- cassette-preload.mjs: ~80-line subprocess preload that boots seinfeld
via createCassette(), replacing the old 450-line preload.mjs. The
subprocess writes its cassette file directly; no parent recorder server needed.
- cassette-filters.mjs: per-scenario FilterSpec registry, porting the
AI-SDK volatile-field normalizer and Mistral agent-name normalizer to
seinfeld's FilterConfig API.
- scenario-harness.ts: drops startCassetteRecorderServer, parseCassetteMode,
and all parent-side recorder wiring. record-missing mode replaced with
plain record (seinfeld overwrites cassette files in full).
- 26 cassette files migrated from the legacy format to seinfeld's format
(version + meta wrapper, body payloads as { kind, value } objects) using
dev-packages/seinfeld/scripts/migrate-from-legacy.mjs.
- cassette-replay scenario removed (covered by seinfeld's own test suite).
- record-cassettes.mjs simplified: always uses record mode, --record-fresh
flag dropped.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
- Run prettier on all cassette JSON files and tsconfig.json - Add dev-packages/seinfeld workspace to knip.jsonc with correct entry points so internal exports are traced from src/index.ts - Remove export keyword from internal-only constants (format/v1.ts intermediate Zod schemas, normalizer/redactor preset objects and header arrays) that are only used within their own module - Remove unused recordResponse export from msw.ts - Remove redundant computeMatchKey re-export from recorder.ts (it is still exported from matcher/index.ts which is what tests import) Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
…oad use AsyncLocalStorage.enterWith() does not propagate through async boundaries created by MSW's request interceptors. When start() is called from a Node.js --import preload, als.getStore() returns undefined in the MSW handler, causing every intercepted request to passthrough to the real network instead of replaying from the cassette. Fix: alongside als.enterWith(ctx), also set a module-level processLevelCtx. The handler checks als.getStore() first (so concurrent use() calls via vitest's beforeEach still work correctly) and falls back to processLevelCtx. stop() clears it when the cassette is torn down. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
seinfeld's createJsonFileStore appends .cassette.json when resolving cassette file paths. Rename all cassette files accordingly and update the extension references in tags.ts and scenario-harness.ts. Also simplify cassette-preload.mjs to pass the __cassettes__ directory to createJsonFileStore rather than a full file path, letting the store handle name→path resolution naturally. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
…onversion Two issues in the legacy cassette converter: 1. SSE chunks were stored as raw HTTP DATA frame fragments in the old format, not as complete SSE events. The converter was mapping each old fragment to a new seinfeld chunk, causing mid-event splits. The AI SDK then saw truncated JSON fragments as SSE event bodies and failed to parse them. Fix: concatenate all fragment bytes first, then split on \n\n to produce complete SSE events as seinfeld's format requires. 2. The huggingface cassette stored URLs with percent-encoded brackets (%5B%5D) but the HuggingFace SDK sends them unencoded ([]). Seinfeld's default matcher uses strict string comparison on the full URL, so the encoding difference caused spurious misses. Fix: add URL normalization through the WHATWG URL parser to seinfeld's default filter preset, applied to both cassette candidates and incoming requests before comparison. All 25 cassettes re-converted from the original legacy format with the corrected SSE splitting logic. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Four distinct root causes addressed:
1. Empty body mismatch (HuggingFace, all GET requests)
The legacy format stored zero-length request bodies as
{ bodyEncoding: "utf8", body: "" }. The converter was producing
{ kind: "text", value: "" }, but seinfeld's encodeBody() returns
{ kind: "empty" } for incoming zero-length requests. deepEqual
comparison failed kind !== kind.
Fix: converter now returns { kind: "empty" } for empty text bodies;
seinfeld's bodyEqual normalizes { kind: "text", value: "" } to
{ kind: "empty" } before comparison.
2. cassetteEngaged wrong file extension (OpenAI assertions)
openai-instrumentation/assertions.ts:618 checked existsSync for
${snapshotName}.json but cassette files are *.cassette.json.
cassetteEngaged was always false, causing the strict
expect(span?.output).toBeUndefined() branch to run during cassette
replay (which always has a defined output from buffered SSE).
Fix: change extension to .cassette.json.
3. AI SDK v5/v6 Responses API body drift
Cassettes were recorded with older AI SDK minor versions. Newer
versions (5.0.82, 6.0.1) add Responses API default fields like
store, background, truncation, reasoning, service_tier, metadata,
etc. deepEqual on the full request body failed for 3 of 7 entries.
Fix: add comprehensive ignoreBodyFields for known Responses API
drift fields to the ai-sdk-instrumentation and ai-sdk-otel-export
filter specs.
4. Cassette SSE chunking and prettier formatting
All 23 cassettes re-converted from original git sources to pick up
both the empty-body fix and the previously-fixed SSE chunk splitting.
Prettier applied to all cassette JSON files.
Pre-existing failures NOT addressed (require re-recording with API keys):
- Mistral: no cassette directory
- Google ADK: stale snapshots
- Cohere 7.20.0+/8.0.0: no cassettes for newer versions
- js-provider-tests: Anthropic streaming LLM output flakiness
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Three additional root causes: 1. URL percent-encoding normalization Node.js v20+ does NOT re-encode `[` and `]` in query strings when you call `new URL(url).href`. The seinfeld default filter was using .href for canonicalization, but the cassette stored URLs with %5B%5D while incoming requests from the HuggingFace SDK use unencoded []. Fix: use URLSearchParams.toString() to rebuild the query, which always percent-encodes brackets consistently on all Node.js versions. 2. SSE response as ReadableStream (TTFT metric missing in OpenRouter) Seinfeld was returning SSE responses as a single ArrayBuffer. The old preload returned a ReadableStream that yielded one chunk per pull. The Braintrust instrumentation measures time_to_first_token by tracking when the first chunk arrives from the stream — if all chunks arrive at once (as a single ArrayBuffer read), the TTFT tracking code never fires and the metric is undefined. Fix: return a ReadableStream for SSE bodies in buildResponse(), yielding each SSE event as a separate chunk, matching the old preload's behavior. 3. AI SDK v5/v6 body comparison too strict The cassette was recorded with ai@5.0.82 and @ai-sdk/openai@2.0.57. Despite same pinned versions, 3 of 6 requests to /v1/responses miss because their request bodies contain fields that differ from the cassette (tool schema format, SDK default fields, etc.). Fix: use ignoreBodyFields: ["**"] for ai-sdk-instrumentation and related filters to strip all body fields and match purely by URL + method + callIndex. This is safe because the scenario always makes requests in the same deterministic order that matches the cassette recording order. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
…tries Two issues introduced by rebasing onto main commits 617889c and f819659: 1. cohere scenario.impl.mjs was missing useV2Namespace, getOperationName, getOperationClient and useV2Api additions from 617889c (fix cohere: wrap v2 subclient). The rebase conflict resolution took the wrong version, dropping those additions. Restore from origin/main so the scenario produces cohere-v2-chat-operation span names that match the snapshot. 2. f819659 (fix groq: capture reasoning for groq reasoning models) added a new groq-reasoning-stream-operation to the groq scenario that makes a streaming request to the qwen/qwen3-32b model with reasoning_format:parsed. The groq cassettes had no entry for this request, causing cassette misses. Add a synthetic streaming entry to both groq-v1-auto and groq-v1-wrapped cassettes with a realistic SSE response including reasoning content and completion_reasoning_tokens in the usage stats. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
The ADK SDK now emits separate start events (metrics only) and end events (with input/output/metrics) for each span. Update snapshots to capture the two-phase emission pattern and include the tool: get_weather span. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
- ai-sdk: remove "**" wildcard from ignoreBodyFields so stream vs
non-stream requests match the correct cassette entries; the wildcard
was causing non-streaming calls to receive SSE responses
- groq: split synthetic reasoning SSE entry into separate content and
stop/usage chunks so x_groq.usage is captured; fix entry 3 callIndex
from 2 to 3
- cohere: rewrite v7-14-0 cassette from /v1/{chat,embed,rerank} to
/v2/{chat,embed,rerank} to match what client.v2.* actually calls
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Picks up the normalizeModelNames change from main (9dab2c4) which normalizes model names to "<model>" in snapshots to avoid flakiness when the model name changes between test runs. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
- Cohere v7-14-0 cassette: add cached_tokens field to message-end event - Groq v1 cassettes (auto + wrapped): add top-level usage field mirroring x_groq.usage - HuggingFace log-payload snapshots: remove _is_merge marker rows and consolidate span data into single records per span Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…etrics Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Add cassette entries for output-object, embed, embedMany, cache fill/reads, deny-output-override, generate-object, stream-object, agent-generate/stream, attachment, Anthropic cache metrics, and Cohere rerank (v6). Restore the "**" body-wildcard in the ai-sdk cassette filter so matching is callIndex-only, making cassettes resilient to SDK version changes. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…oogle/gemini-2.5-flash-lite Add body-wildcard filters for openrouter-agent-instrumentation and openrouter-instrumentation so matching is callIndex-only, resilient to SDK version changes. Update callModel() cassette response entries from openai/gpt-4o-mini-2024-07-18 to google/gemini-2.5-flash-lite to match the CALL_MODEL constant change in 89d23f1. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Revert the incorrect removal of the tool: get_weather span and token metrics (completion_tokens, prompt_tokens, tokens) from the google-adk snapshots. CI confirmed these are still emitted at runtime. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…yload The Google ADK instrumentation emits the user input on both the start and end phases of the Google ADK Runner span. The start-phase log payload entry was missing the input block. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
@cursor/sdk 1.0.12 adds a thinkingMessage step before the assistantMessage in cursor_sdk.step_types. Update the pinned version and auto-hook snapshot. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…apshot The thinkingMessage step type is model-dependent and only appears when the model reasons before responding, making it unreliable as a snapshot assertion. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Canary tests run against @latest provider SDK versions with real API keys. Previously, if a pinned cassette file existed for the same variant key (e.g. anthropic-v0800), the cassette layer would activate in replay mode for the canary run. The latest SDK version may send slightly different request bodies, causing cassette misses. A miss returns HttpResponse.error(), triggering SDK retry logic and eventually hitting the subprocess timeout. Setting BRAINTRUST_E2E_CASSETTE_MODE=passthrough ensures the cassette layer is a no-op during canary runs so requests reach the real provider APIs. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Luca Forstner (lforst)
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A few things I think we could clean up but otherwise lgtm
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| // Load `.env` from the repo root (and `.env.local` if present, for | ||
| // developer-local overrides) into process.env so that local test runs and | ||
| // recordings can pick up provider keys without exporting them in the | ||
| // shell. Existing env values are preserved (override: false). | ||
| const setupDir = path.dirname(fileURLToPath(import.meta.url)); | ||
| const repoRoot = path.resolve(setupDir, ".."); | ||
| loadDotenv({ path: path.join(repoRoot, ".env"), override: false, quiet: true }); | ||
| loadDotenv({ | ||
| path: path.join(repoRoot, ".env.local"), | ||
| override: false, | ||
| quiet: true, | ||
| }); | ||
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mise should be taking care of loading .env
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| const env = { | ||
| ...process.env, | ||
| BRAINTRUST_E2E_CASSETTE_MODE: "record", |
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I feel like instead of having this entire file we can just set the env var in the test:e2e:record script?
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| Then run again in `BRAINTRUST_E2E_CASSETTE_MODE=replay` with no provider keys to confirm the cassette is sufficient. | ||
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| - Volatile fields in request bodies (e.g. AI-SDK `experimental_generateMessageId`) need a per-scenario filter. Add the scenario name and a `FilterSpec` to `e2e/helpers/cassette-filters.mjs`. The cassette layer is backed by `@braintrust/seinfeld` (`dev-packages/seinfeld`); the preload entry point is `e2e/helpers/cassette-preload.mjs`. |
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Can we add to the skill that the agent should always check the cassettes for potentially leaked API keys when generating them and redact them if they would be leaked if committed?
| import { z } from "zod"; | ||
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| /** | ||
| * Zod schema for cassette format version 1. |
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Is there a reason for us to have versions?
| @@ -0,0 +1,300 @@ | |||
| #!/usr/bin/env node | |||
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Do we still need this file?
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| MIT License | |||
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| Copyright (c) 2026 Stephen Belanger | |||
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I feel like we don't need a license here because we already have one in the repo and this should most likely be Braintrust LLC if anything
| "devDependencies": { | ||
| "@braintrust/langchain-js": "workspace:^", | ||
| "@braintrust/otel": "workspace:^", | ||
| "@braintrust/seinfeld": "workspace:^", |
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I don't know how I feel about having to build that package before being able to run e2e tests but I won't block on this now.
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can we remove this file now that we've migrated this?
| const normalizerName = config.normalizerName ?? scenarioName; | ||
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| return { | ||
| ...getProviderKeyPlaceholders(), |
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I think we need to gate this on cassetteMode === "replay"
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| export const CASSETTE_FILTERS = { | ||
| default: "default", | ||
| "ai-sdk": ["default", AI_SDK_VOLATILE_FIELDS], | ||
| "ai-sdk-instrumentation": ["default", AI_SDK_VOLATILE_FIELDS], | ||
| "ai-sdk-otel-export": ["default", AI_SDK_VOLATILE_FIELDS], | ||
| "mistral-instrumentation": ["default", MISTRAL_VOLATILE_FIELDS], | ||
| "openrouter-agent-instrumentation": ["default", OPENROUTER_VOLATILE_FIELDS], | ||
| "openrouter-instrumentation": ["default", OPENROUTER_VOLATILE_FIELDS], | ||
| }; |
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can we make these filters configured in the scenario? So they are closer to the integration they are testing instead of being global like this?
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| `'paranoid'` redacts credential headers, common credential field names at any JSON depth (`apiKey`, `token`, `secret`, `password`, `authorization`), and Bearer / `sk-` style tokens in text bodies. | ||
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| To detect misconfigurations at record time, add `strict: true`: |
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this feels like it should just be the default behaviour. Also feels like paranoid should be the default behaviour. I would only change redact if I'm removing something imo.
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Summary
Adds an inbound provider HTTP capture/replay layer (cassettes) to the e2e test suite so hermetic CI runs replay recorded traffic instead of hitting live provider APIs. Built on MSW (already in the workspace as a dev dep for
integrations/langchain-jsandintegrations/otel-js) plus ~600 LoC of cassette-format/matcher/recorder glue.E2E scenarios previously hit live provider APIs on every CI run. Flakiness sources: rate limits, transient 5xx, model-output drift breaking exact-string snapshot fields. With this layer:
__cassettes__/<variantKey>.json.BRAINTRUST_E2E_CASSETTE_MODE=record-missing. CI never records.mock-braintrust-server.tsand__snapshots__/are untouched. Cassettes are the inbound mirror: provider→SDK, where snapshots are SDK→Braintrust.Status: ~506 tests passing in hermetic mode across 25 scenarios, 2 of 3 consecutive runs deterministic (the third had an unrelated
turbopack-auto-instrumentationNext.js compile timeout flake — not introduced by this PR).Architecture
mock-braintrust-server.ts(parent process HTTP server)__snapshots__/*.jsoncassette/preload.mjsboots an MSWsetupServer()in subprocess__cassettes__/<variantKey>.jsone2e/helpers/cassette/preload.mjs— loaded into each scenario subprocess vianode --import=<preload>. Boots MSW synchronously and intercepts provider HTTP traffic.cassetteTagsFor(import.meta.url, variantKey)auto-tags scenarios withhermeticbased on cassette file presence — opt-in is by committing the cassette.Cassette modes (
BRAINTRUST_E2E_CASSETTE_MODE)replay(default in CI): match or throwCassetteMissError.record: overwrite cassette fresh.record-missing: match if possible, else live + record. Standard re-record loop.passthrough: bypass cassettes entirely (local debugging).Recording safeguards
400 API_KEY_INVALIDresponses. The 400 case was added after.authorization,x-api-key,api-key,x-goog-api-key,cohere-api-key, cookies, request IDs, rate-limit windows,content-encoding, etc. before persisting. (Caught a near-miss on this PR — the initial commit leakedx-api-keyfor Anthropic; volatile-header set has been broadened and a scrub run removed leaked values.)new Headers(request.headers)silently drops most headers when the source is an MSW-intercepted request (Authorization included). The forwarder copies viaforEachinstead. This one bug was responsible for the bulk of the recording failures during initial migration (every Mistral 401, plenty of others).Scenarios with complete cassettes (hermetic green)
anthropic-instrumentation(6 variants)openai-instrumentation(3 variants)claude-agent-sdk-instrumentationopenrouter-instrumentation(2 variants)ai-sdk-instrumentation(4 variants)ai-sdk-otel-export(2 variants)groq-instrumentation(2 variants)huggingface-instrumentation(3 variants)openrouter-agent-instrumentationwrap-langchain-js-tracescassette-replay(meta-scenario validating record→replay loop end-to-end)cohere-instrumentationv7-14-0 (1 of 5 variants — see below)Scenarios still missing cassettes (auto-skipped in hermetic mode)
These auto-skip cleanly because
cassetteTagsForonly applies thehermetictag when the cassette file is present. CI does not fail on them today; they need a follow-up record run with working credentials.mistral-instrumentation— needs re-record after rebasemain, the existing mistral cassettes no longer match: main extended the mistral scenario with new thinking/reasoning model coverage (NATIVE_REASONING_MODEL,ADJUSTABLE_REASONING_MODEL) that wasn't in the older scenario shape the cassettes were recorded against.cohere-instrumentationalready does —COHERE_RECORD_THROTTLE_MS = 60_000) or running mistral variants serially with longer waits between calls.scenario.impl.mjsand runBRAINTRUST_E2E_CASSETTE_MODE=record-missing pnpm --filter=@braintrust/js-e2e-tests vitest run scenarios/mistral-instrumentation.google-genai-instrumentation— Gemini quota exhaustedRESOURCE_EXHAUSTED 429).400 API_KEY_INVALIDresponses; those were detected and deleted in this PR. The skip-list now rejects 400 to prevent recurrence.BRAINTRUST_E2E_CASSETTE_MODE=record-missing pnpm --filter=@braintrust/js-e2e-tests vitest run scenarios/google-genai-instrumentation.cohere-instrumentation— per-MONTH quota exhausted (4 of 5 variants)"You are past the per-month request limit for this model, please wait and try again later."This is monthly, not daily — recovers on the next billing cycle.v7-14-0variant is fully recorded (chat + chat-stream + embed + rerank) and replays green. The 4 remaining variants (v7-20-0,v7-21-0,v7default,v8) auto-skip until re-recorded.COHERE_RECORD_THROTTLE_MS) to land each call in a fresh budget window once quota is restored — but the throttle can't help with monthly exhaustion.google-adk-instrumentation— model-behavior drift, unrelated to cassette layer__cassettes__/files in this PR, so it auto-skips in hermetic mode. There is pre-existing snapshot drift unrelated to this PR which should be triaged independently.Risks / things to watch
claude-agent-sdk-instrumentationandai-sdk-instrumentationhave the largest cassettes (long transcripts). This is intentional — diff-ability matters for review, and we want byte-identical replay.e2e/README.md("Cassettes" section) and.agents/skills/e2e-tests/SKILL.md.nextjs-instrumentation,turbopack-auto-instrumentation, and OTEL-only scenarios. Those need separate preload mechanisms; they continue running as before (or are already hermetic-ish via different machinery).Test plan
pnpm --filter=@braintrust/js-e2e-tests exec vitest run --tags-filter=hermetic— green (506 passed, 396 skipped, 0 failed)pnpm run formattingcleanpnpm run lint— 0 errorsx-api-key,api-key,x-goog-api-key,authorization, etc. all stripped)🤖 Generated with Claude Code