rea/docs/javascript-runtime-observation.md

Passive Node and Electron runtime observation

REA can attach to an already-running Node.js or Electron V8 Inspector target and retain script-load and execution-context metadata. The list_javascript_runtime_targets and observe_javascript_runtime MCP tools have equivalent rea list-javascript-runtime-targets and rea observe-javascript-runtime commands. Successful calls return deterministic Evidence.

This authority is disabled by default and is separate from browser CDP, Electron file-page inspection, Process Capture, and controlled JavaScript replay:

export REA_V8_INSPECTOR_OBSERVE_ENABLED=true
export REA_V8_INSPECTOR_ENDPOINTS_JSON='["http://127.0.0.1:9229"]'
export REA_V8_INSPECTOR_FILE_ROOTS_JSON='["/absolute/path/to/app"]'
export REA_V8_INSPECTOR_ALLOWED_ORIGINS_JSON='[]'

rea list-javascript-runtime-targets http://127.0.0.1:9229 \
  --json
rea observe-javascript-runtime http://127.0.0.1:9229 TARGET_ID \
  --runtime-kind node --json

At least one canonical file root or exact HTTP(S) origin is required. Discovery is restricted to a literal-loopback HTTP endpoint. A target must match the exact requested target ID, expose a same-port WebSocket reported by the approved discovery endpoint, and remain inside the requested file or origin scope. Targets already marked attached are rejected rather than displacing another debugger. Canonical file paths are checked after symlink resolution. Excluded locations are counted but never retained.

list_javascript_runtime_targets returns every approved target in one inline array. The Inspector discovery response-size ceiling remains internal; an oversized response fails explicitly.

For the MCP follow-up call, pass the discovery Evidence ID and selected target ID to observe_javascript_runtime. REA reuses the endpoint and file/origin scope from that retained discovery Evidence, checks the selected ID against its target list, and reapplies permission policy. The agent does not repeat roots or origins. The CLI continues to accept its endpoint and scope arguments directly.

Passive protocol boundary

The provider sends exactly two protocol commands:

• Runtime.enable
• Debugger.enable

It never sends Runtime.evaluate, reads script source, installs breakpoints, pauses or resumes execution, calls Runtime.runIfWaitingForDebugger, launches the target, instruments JavaScript, or invokes Electron APIs. Closing a call closes only REA's WebSocket.

The direct observations are:

• Debugger.scriptParsed, establishing that a bounded script location was parsed in the observed execution context;
• Debugger.scriptFailedToParse, retained only as a bounded invalid-script count;
• Runtime.executionContextCreated, Runtime.executionContextDestroyed, and Runtime.executionContextsCleared, establishing context lifecycle within the capture window.

The Inspector protocol does not directly expose require/import caller edges, EventEmitter emissions or listener invocation, Electron IPC messages or handlers, or script-unload events. Those facts remain explicit unknowns. scriptParsed proves script presence, not the importing module, feature execution, initialization order, or causality.

Node and Electron roles

The caller declares one role: node, electron-main, electron-preload, or electron-renderer. Node and Electron-main declarations require a protocol target of type node; preload and renderer declarations require page. Inspector does not authenticate the operating-system PID or distinguish an Electron role, so Evidence records the role authority as caller-declared-unverified.

Electron main, preload, and renderer behavior can therefore be observed only as separate approved Inspector targets. The provider does not infer that two targets belong to the same Electron application.

Capture and determinism

Every observation records its time window and returns all valid script and execution-context events received during it. Per-location protocol validation remains in force. Scripts are authorized after capture, deduplicated by stable metadata, and canonically sorted. Wall-clock timestamps and protocol script IDs are excluded from the durable result, so identical inputs and captured metadata produce the same Evidence ID.

Inspector attach is inherently incomplete. Enabling Debugger reports known and uncollected scripts, but scripts collected before attachment may be missing. Absence from the observation window never proves that a script or behavior does not occur.

Static correlation

Pass the resulting observation Evidence and an analyze_javascript_application Evidence record to reconcile_javascript_runtime. The reconciliation accepts this provider alongside passive web and Electron page captures. Exact approved file or URL mappings can correlate script presence with JavaScript Application Graph assets. Because this provider never reads source bytes, matches normally use a unique authorized location and remain weaker than captured-byte identity. Builtin node: scripts remain runtime-only nodes unless a future explicit static authority models them.