cold-start: tune Sentry sampling and Vercel function limits

[x0ba]

Stack Context

This stack reduces Vercel cold-start time by shrinking the shared SvelteKit server boot path and isolating heavy agent/GitHub dependencies.

Why?

Full Sentry trace sampling and server instrumentation added startup overhead on every cold boot. This PR lowers production sampling, disables Sentry server tracing on Vercel, and sets maxDuration on long-running agent and webhook routes.

Test plan

• Confirm Sentry still receives errors in production
• Confirm agent run and webhook routes respect extended timeouts on Vercel

[vercel]

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Project	Deployment	Actions	Updated (UTC)
flightlog	Ready	Preview, Comment	May 28, 2026 4:59pm

[x0ba]

• cold-start: tune Sentry sampling and Vercel function limits #45 👈 (View in Graphite)
• cold-start: split Neon and pg database drivers #44
• cold-start: lazy-load agent runner heavy dependencies #43
• cold-start: split regression execution into executor module #42
• cold-start: decouple webhook registration from server hook #41
• staging

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[greptile-apps]

Greptile Summary

This PR reduces Vercel cold-start overhead by disabling SvelteKit's experimental OpenTelemetry server tracing on Vercel (while keeping Sentry initialisation intact), lowering Sentry's production trace sample rate from 100 % to 10 %, and adding export const config = { maxDuration } to long-running API routes using the @sveltejs/adapter-vercel Config API.

• svelte.config.js: tracing.server is gated on !VERCEL, but instrumentation.server remains true, so Sentry.init() still runs and sentryHandle() / handleErrorWithSentry() in hooks.server.ts continue to capture errors in production.
• src/instrumentation.server.ts: tracesSampleRate drops from 1.0 to 0.1 in production builds via import.meta.env.PROD, cutting performance-tracing ingestion cost while preserving error and log capture.
• Seven route files add per-route maxDuration values (60 s for the GitHub webhook, 300 s for agent, stream, and all regression endpoints), which the adapter writes directly into each function's Vercel Build Output API config.

Confidence Score: 5/5

Safe to merge — the changes are narrowly scoped to Vercel configuration and do not touch any application logic.

SvelteKit's OpenTelemetry tracing is disabled only on Vercel builds, while instrumentation.server remains true, keeping Sentry initialised and error reporting fully operational. The trace sample-rate change is a build-time constant swap with no runtime risk. All maxDuration exports use the correct adapter-level API, which is the authoritative path for the Build Output API. No application logic was changed.

No files require special attention.

Important Files Changed

Filename	Overview
svelte.config.js	Disables SvelteKit's server-side OpenTelemetry tracing on Vercel via process.env.VERCEL !== '1'; instrumentation.server stays true so Sentry is still initialised and error reporting is unaffected.
src/instrumentation.server.ts	Lowers tracesSampleRate to 0.1 in production via build-time import.meta.env.PROD replacement; Sentry error and log capture is unchanged.
src/routes/api/agent-runs/+server.ts	Adds maxDuration: 300 adapter config; appropriate for a route that spawns long-running agent work.
src/routes/api/github/webhook/+server.ts	Adds maxDuration: 60; reasonable for a webhook handler that may do async GitHub API work.
src/routes/api/runs/[id]/stream/+server.ts	Adds maxDuration: 300 for the SSE streaming endpoint; necessary to keep the serverless function alive for the full agent-run lifetime.
src/routes/api/regression/suites/[id]/runs/+server.ts	Adds maxDuration: 300; the POST schedules a regression run and GET lists runs — both are quick DB operations, but 300 s is harmless and keeps the file consistent with sibling routes.
src/routes/api/regression/runs/[id]/cases/[caseId]/complete/+server.ts	Adds maxDuration: 300; appropriate for a route that completes a regression case run which may involve evaluation logic.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Vercel Cold Start] --> B{VERCEL eq 1?}
    B -- Yes --> C[tracing.server = false\nSvelteKit OTEL disabled]
    B -- No --> D[tracing.server = true\nSvelteKit OTEL enabled]
    C --> E[instrumentation.server = true\nSentry.init called]
    D --> E
    E --> F{PROD build?}
    F -- Yes --> G[tracesSampleRate = 0.1]
    F -- No --> H[tracesSampleRate = 1.0]
    G --> I[Sentry errors and logs captured]
    H --> I
    subgraph Route maxDuration
        J[agent-runs: 300s]
        K[runs stream: 300s]
        L[github webhook: 60s]
        M[regression routes: 300s]
    end

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[x0ba]

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@greptile review

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Merge activity

• May 28, 4:49 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• May 28, 4:58 PM UTC: Graphite rebased this pull request as part of a merge.
• May 28, 4:58 PM UTC: @x0ba merged this pull request with Graphite.