rea/docs/electron-observation.md

Electron file-page observation

REA can attach to an Electron/Chromium CDP endpoint and inspect existing file:// renderer pages without evaluating JavaScript or invoking Electron APIs. The request supplies the endpoint directly; REA accepts only literal-port loopback HTTP endpoints. Selecting an endpoint exposes every Electron target it serves, including local file paths and page metadata.

This passive runtime surface is distinct from the target-free static analyze_javascript_application workflow. Static analysis reads a local ASAR or extracted directory without executing application code. Passive observation inspects an existing Electron page. The results keep static inferences and runtime observations distinct. Use the separate reconcile_javascript_runtime workflow when both Evidence sets already exist.

Target boundary

The request supplies a literal-port loopback endpoint and, for inspection, a target ID. REA accepts local hostless file:// URLs that resolve to regular files, including pages a packaged application serves from inside app.asar. For those, the first .asar path component that is a regular file is the archive, the remainder must name a regular file in its header, and the reported path is the canonical archive path joined with that member. Remote hosts, encoded path separators, ASAR directories or links, and nonexistent paths are rejected. The endpoint exposes every eligible target and its local path metadata.

Workflow

list_electron_targets returns every eligible target served by the supplied endpoint in one inline array.

For the MCP follow-up call, pass the same literal-loopback endpoint and the selected target ID to inspect_electron_page. REA rediscovers targets and validates the ID against the live endpoint before inspection.

rea list-electron-targets http://127.0.0.1:9223 --json
rea inspect-electron-page http://127.0.0.1:9223 TARGET_ID \
  --observation-ms 100 --json

Script content is excluded by default. Setting include_script_sources in the request returns the selected target's script sources:

rea inspect-electron-page http://127.0.0.1:9223 TARGET_ID \
  --include-script-sources \
  --json

The normalized result contains canonical local paths, frame and DOM structure, resource metadata, stable script/resource identities, explicit completeness, and content-addressed script artifacts. Script metadata retains its execution-context frame ID when CDP supplies one. The capture also inventories worker, service-worker, and shared-worker targets with validated opener-target and parent-frame IDs. Worker discovery uses passive target metadata; REA does not attach to or execute code in those targets. Collection counts and aggregate script-source bytes are not capped. Like every target, frame, script, and resource, a worker URL must resolve to a local file before it is retained. Relationship IDs improve attribution but do not prove which static module started a worker or that its work completed.

Inspection does not retain DOM values, execute renderer code, navigate, click, invoke Electron IPC, close a target, or terminate the application.

Active Electron scenarios

The scenario request supplies the Electron executable and application entry point, plus any arguments and actions. The application root defaults to the entry point's parent directory and can be supplied when the app uses a different root. REA launches that executable through the official Playwright Electron API and owns its lifetime. It accepts click/wait actions, window-targeted renderer reload/crash actions, and synthetic open-url or second-instance deep-link delivery. It records capture-scoped window and WebContents identities, process metrics, and IPC channel and value-shape metadata. Payload values are not retained.

Run the real fixture verifier with an operator-provided Electron runtime:

REA_ELECTRON_EXECUTABLE=/absolute/path/to/electron npm run verify:electron

This operation actively launches and interacts with the selected target. It is not a passive CDP observation. The owned process keeps normal host filesystem and network privileges, so lifecycle ownership does not make it a sandbox.

The CLI and MCP surfaces accept the same schema. For a JSON request file:

rea capture-electron-scenario scenario.json --json

The result records action status and targets, correlated app/window/WebContents, preload, session, navigation, shell, permission, popup, download, protocol, native-addon, process, and IPC timeline events. IPC channels and argument-shape metadata retain their observed lengths; payload values are never retained. Renderer crash/restart and deep-link actions are synthetic scenario controls; their attempted and observed outcomes remain in the timeline. The active hook blocks and records external shell/navigation, permission, download, popup, updater, and OS-integration effects. The timeline is explicitly partial when attachment starts after application activity. The startup has a 60-second deadline. Actions wait until completion or request cancellation; a click whose target never appears remains pending until cancelled. CLI SIGINT/SIGTERM requests cancellation and awaits owned-process cleanup. Window IDs, URLs, and cached titles come from one main-process Electron snapshot, so a crashed renderer does not require a successful renderer-side title query. Window instrumentation uses Electron's window-created event, including runtimes with a read-only BrowserWindow export. Preload configuration comes from the window's runtime metadata, including Electron's optional internal preload descriptor when web preferences omit it. This descriptor is verified on Electron 44.7.0; runtimes that expose neither representation retain an unavailable path. A configured path or working IPC handler does not prove preload execution. If cleanup cannot be verified, the error retains collected observations in details.partial_observation and marks their application cleanup unverified. Cleanup uncertainty does not authorize signaling unrelated processes.

The real verifier exercises compiled CLI and stdio MCP discovery, page/script inspection, static/runtime reconciliation, active observation, and CLI SIGTERM cleanup before checking the IPC, renderer crash/reload, utility/child-process, deep-link, and blocked-effect fixture. A cleanup error keeps the full lane failed even when the retained capture contains useful observations.

Active Electron Evidence can also be supplied to reconcile_javascript_runtime. That projection is intentionally target-only and partial: it binds the selected application path and capture outcome to the static graph, while frames, scripts, workers, and execution claims remain unavailable until a separate passive runtime capture provides them.

ASAR observation reads the header through one open file handle, validates its declared lengths against the archive size, and limits encoded JSON headers to 16 MiB before parsing. The header cache also retains at most 16 MiB of encoded headers across eight archives. Oversized headers produce a scope refusal.