debugging-cursor-byok

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name: debugging-cursor-byok description: Use when debugging this repository's Cursor BYOK behavior: workbench hook install failures, missing models, BYOK/official misrouting, remote workspace regressions, stalled tool calls, Read offset/limit complaints, MCP completion hangs, reconnect loops, or suspicious extension-host CPU.

Debugging Cursor BYOK

This repository tends to break at five boundaries. Find the first broken boundary before changing code:

1. install seam (scripts/install-workbench-hook.js, patched Cursor bundle)
2. route decision (official model vs BYOK model)
3. run/session correlation (RunSSE/Run + BidiAppend + request ids)
4. native Cursor tool completion (exec ids, interaction responses, client-tool completions)
5. provider-visible schema/result text (what the upstream model actually saw)

Start Here

• Reproduce once in a real Cursor window before editing code. Prefer one official-model control run and one BYOK run for the same task.
• Capture requestId, conversationId, toolCallId, and, when present, execId from BYOK logs.
• Use references/symptom-map.md to choose the boundary.
• Use references/log-signals.md to interpret specific log lines.

Evidence Rules

• Trust Cursor logs, BYOK logs, current source, and current tests over model narration. A provider claiming "Read was truncated" is not evidence by itself.
• For tool issues, inspect all three layers: provider tool args, native exec message emitted by the hook, and Cursor exec result returned to the provider.
• For UI hangs, do not stop at toolCallStarted; confirm the terminal sequence reaches toolCallCompleted and stepCompleted.
• For remote-only bugs, verify the same scenario locally first.
• For high CPU, isolate by disabling the extension and restarting Cursor. A window under active accessibility or Computer Use inspection is not a clean CPU signal.

Fast Paths

• Hook / install / reconnect after Cursor update:
  • run npm run preflight:cursor
  • if supported, run npm run install:cursor
  • only use npm run restore:cursor when a pristine backup was captured earlier
  • read docs/routing-hook.md and docs/install-config.md
• Model missing or wrong route:
  • inspect src/runtime/models.js, src/server/http.js, and src/workbench-hook.js
  • run the model/routing tests listed in the symptom map
• Tool stalls, empty results, or stuck spinner:
  • inspect drainRunInput, /byok/local-tool-result, /byok/interaction-response, /byok/client-tool-completion, and /byok/exec-map
  • verify the relevant waiter in src/runtime/state.js resolves
• Read / Grep / Glob complaints:
  • verify the schema in src/runtime/tools.js
  • verify provider-visible result text in src/server/provider-adapter.js
  • verify native exec payloads in src/workbench-hook.js
• MCP problems:
  • separate native MCP exec completion from MCP auth and provider-visible sanitized names
  • inspect tests/byok-hook-mcp.test.js, tests/byok-server-mcp-cache.test.js, and tests/interaction-bridge.test.js
• Remote workspace regressions:
  • inspect tests/byok-extension-activation.test.js and /byok/workspace-roots
  • verify the same path on a remote window, not only locally

When Comparing With old

The old branch is a reference for intended behavior, not proof that a direct port is correct. If a fix idea comes from old, re-prove it against current main source paths and current tests before shipping it.

Read Next

• docs/architecture.md
• docs/routing-hook.md
• docs/provider-tools.md
• docs/verification.md
• references/symptom-map.md
• references/log-signals.md