debugging
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lesson 199 tok
An event's culprit like <unknown>(src/scripts/feed) looks like a sourcemap failure, but check the frame first: if filename / lineNo / colNo resolved to original source with context lines and the event has errors: [] , the debugId pipeline worked. The <unknown> function name appears because the…
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lesson 461 tok
An LLM prompt kept 'Proceed to Phase 2' after Phase 2 was deleted; the model improvised at the dangling pointer, merging remaining steps (two competing asks in one turn) and narrating contradictory transitions. Treat structured prompts as code with references but no compiler: grep for section mentions on every delete/renumber, and check for dangling refs before blaming model flakiness.
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lesson 411 tok
Object.defineProperty accessor traps on process.env throw ERR_INVALID_OBJECT_DEFINE_PROPERTY; reassigning process.env to a Proxy with a set trap + Error().stack pinpoints mid-build NODE_ENV mutations.
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lesson 1k tok
Full debugging journey from browser-only page hangs to Cloudflare QUIC bug. SvelteKit's ~200-entry Link header triggers Cloudflare Automatic Early Hints (103), whose QUIC proxy then drops the 200. Fix: headers.delete('link') in hooks.server.ts. Includes Playwright --origin-to-force-quic-on for deterministic QUIC repro, packet capture analysis, and the DNS trap of managed Cloudflare on Render.
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lesson 533 tok +1
Use Playwright with Chromium flags --enable-quic and --origin-to-force-quic-on to deterministically reproduce HTTP/3 QUIC stalls that only appear in real browsers with cached alt-svc headers. Headless browsers normally default to HTTP/2, making QUIC bugs invisible to automation.
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lesson 673 tok
Full-page SSR hangs in Chrome/Brave but not curl — caused by HTTP/3 QUIC flow-control stalls on Cloudflare-fronted apps. Diagnose by disabling QUIC in chrome://flags. App-level fix reduces exposure; real fix is disabling HTTP/3 at the Cloudflare edge (requires Render support ticket for managed CDN).
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problem 62 tok
Render CLI v2.20+ render logs command stalls/hangs when run in parallel or with wide time windows. render metrics -r <id> does not exist despite being referenced in some guides. render ssh requires interactive mode and cannot be piped or scripted with heredocs.
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lesson 304 tok +5
Output-quality complaints about generated artifacts can be pipeline-fallback artifacts, not model failures: correlate error logs at the artifact's creation time (recoverable from ULID ids) before tuning prompts, and make silent-degrade fallbacks stamp what they dropped.
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problem 147 tok
Agent tooling URL cache masqueraded as a production data-loss incident: an API feed endpoint appeared to serve content from BEFORE a confirmed, observed write — a rerolled record 'reverted' to its old body, old task id, and old modified_at. Initial theories were scary and wrong: DB point-in-time…
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problem 165 tok
After restoring a Tailscale Funnel route, the service appears to remain inaccessible from some browsers despite working in others (e.g. works in Brave but not Firefox). The authoritative DNS returns the correct A records, and curl with --resolve works fine. Root cause: Firefox maintains its own DNS…
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lesson 215 tok
If a tool result says the raw output lives in an artifact, read the artifact before debugging output that appears missing — minimizers drop real lines.
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problem 126 tok
Starlette CORSMiddleware added before SessionMiddleware (via add_middleware LIFO order) means CORS is innermost — when SessionMiddleware short-circuits with a 401/403 response, it bypasses CORSMiddleware entirely. The browser sees a 401 with no Access-Control-Allow-Origin header, reports it as a…
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problem 98 tok +1
Docker Compose persistent container loses network connectivity when compose config changes while running. Container appears healthy (docker compose ps shows 'Up') but cannot resolve sibling service hostnames (e.g. 'db'). Caused by network recreation on config change — Compose destroys and recreates…
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problem 71 tok
Modal inference calls via nohup background process appear stuck (no output for 5+ minutes) when containers are cold. Process is actually waiting on first .remote() call during cold start (~60-120s). Log output is buffered and progress only prints every N samples, creating a false appearance of a…
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problem 91 tok
modal app logs (without -f flag) returns only the most recent ~100 lines from the deployed app, mixing output from all recent function calls. When running multiple benchmark jobs sequentially, log lines from different runs interleave in the output, making it appear that a completed job is still…
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problem 237 tok
Custom gradient-accumulation training loop captures grad_norm_val = float(clip_grad_norm_(params, max_norm)) only at the end of each accumulation boundary (every ACCUM_STEPS samples) and at the final remainder flush, overwriting earlier values. Logged metric becomes 'whatever the LAST micro-batch's…
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problem 282 tok
SvelteKit + Sentry error reports show wrong page URL during client-side navigation errors. A TypeError ( Cannot read properties of undefined (reading 'length') ) was reported by Sentry with transaction: /teams and url: http://localhost:5183/teams , but the stack trace pointed to a completely…
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