fix(cli): give each CLI run its own Chromium session data

[EtienneLescot]

Fixes #1137

Candidate for cherry-pick to release/v2.1.0.

Problem

A CLI process (mcp, export, record, sources, ...) kept Electron's default sessionData, which is userData, so it opened the GUI's Chromium profile. Local Storage, the HTTP cache and the GPU caches are single-process: whichever started first held them. With openscreen mcp running, the GUI's localStorage was in-memory only and every preference stored there was lost on quit.

Fix

• electron/cli/sessionData.ts: before app is ready, each CLI run sets sessionData to a fresh folder, <userData>/cli-sessions/<pid>-<random>. userData itself is unchanged, so projects, recordings, settings and models are still shared with the GUI.
• Concurrent CLI runs each get their own folder, so they do not fight either. A recycled pid never inherits an earlier run's storage.
• Each folder carries an owner.json (host, pid namespace, pid). A run sweeps another run's folder when:
  • its owner is on the same host and pid namespace and its pid is gone (ESRCH only), or
  • its owner file, which a live run refreshes daily, is over a week old. This bounds leftovers from Flatpak, where each sandbox has its own pid namespace.
• A run cannot delete its own folder, since its Chromium holds it until exit. The sweep is async and best-effort.
• If the folder cannot be created, the run keeps the shared profile and logs a warning, instead of hitting Electron's module-load error dialog.

What the CLI loses

Nothing it could rely on. CLI renderers read two localStorage values: custom Google fonts (used for text measuring only, since the native compositor renders exports) and preferSoftwareEncoder in record. They only ever saw them when no GUI or other CLI held the profile.

Validation

• npx vitest --run electron/cli: all pass, including the new sweep-rule tests.
• Both tsc configs and Biome are clean.
• Headless on Windows 11, dev build, while about 12 electron . mcp processes held %APPDATA%\openscreen:
  • two concurrent electron . sources --json both returned done success, with no cache or access-denied lines on stderr;
  • each wrote its own cli-sessions/<pid> folder, holding Local Storage, Cache, GPUCache, DawnGraphiteCache, DawnWebGPUCache and Local State;
  • a planted dead-pid folder on this host was swept; a young foreign-host folder and an ownerless one were kept; the previous run's two folders were swept on the next run.
• GUI not launched, by design (no windows on the desktop). It no longer has a competitor for its profile, since no CLI path opens it any more.

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📥 Commits

Reviewing files that changed from the base of the PR and between 8f6ab38 and 879f112.

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📒 Files selected for processing (2)

• electron/cli/sessionData.test.ts
• electron/cli/sessionData.ts

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📝 Walkthrough

📝 Walkthrough

📝 Walkthrough

📝 Walkthrough

Walkthrough

CLI runs now use PID-specific Chromium session-data directories under the shared user-data directory. Startup also identifies and asynchronously removes session directories for processes that are no longer running.

Changes

CLI session isolation

Layer / File(s)	Summary
Session paths and stale-directory selection electron/cli/sessionData.ts, electron/cli/sessionData.test.ts	Adds PID-specific session paths and selects numeric directory names for exited processes. Tests cover path uniqueness, current and live process exclusions, and non-PID names.
CLI startup isolation electron/cli/sessionData.ts, electron/cli/cliMain.ts, electron/main.ts	runCli isolates session data before continuing startup. The helper creates the session directory, sets Electron’s sessionData path, and starts asynchronous removal of stale directories. The CLI-mode comment now describes the separate Chromium session data.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant runCli
  participant isolateCliSessionData
  participant ElectronApp
  participant FileSystem
  runCli->>isolateCliSessionData: Isolate session data before CLI startup
  isolateCliSessionData->>ElectronApp: Get userData path
  isolateCliSessionData->>FileSystem: Create per-process session directory
  isolateCliSessionData->>ElectronApp: Set sessionData path
  isolateCliSessionData->>FileSystem: Remove stale session directories asynchronously

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Suggested reviewers: petertakahashi

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Merge Risk: 🔵 Low · up to 8f6ab

CLI runs now get their own browser session folders, and folders left by exited runs are cleaned up. In rare setups, cleanup could remove a running CLI's folder or stop CLI startup. Tightening the liveness check and making cleanup best-effort would close these edge cases. The change is otherwise reasonable to merge.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check		Issue #1137 requires separate Chromium session data for CLI runs, shared app userData, and isolation between concurrent CLI runs. runCli calls isolateCliSessionData before app.whenReady(). The i…
Out of Scope Changes check		The changes stay within issue #1137. sessionData.ts implements the required profile isolation and stale-directory cleanup. sessionData.test.ts tests that behavior. The cliMain.ts integration and…
Title check		The title clearly and concisely describes the main change: isolating Chromium session data for each CLI run.
Description check		The description provides a detailed problem statement, fix summary, linked issue, release note, validation steps, and platform-specific testing. It does not follow every template heading or include th…

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[EtienneLescot]

I had started on #1137 in parallel before seeing this PR, so here are a few notes instead of a competing PR. The approach is the same as mine, and the lock and the GUI side both check out:

• Single-instance lock: not affected. requestSingleInstanceLock() keys on userData, not sessionData, and CLI runs still never call it.
• Language-prompt flag: the GUI never moves sessionData, so openscreen.locale, the system-language-prompt flag and the other localStorage prefs stay in <userData>/Local Storage, which is where the GUI expects them.
• Probe, Electron 41.2.1 on macOS: I set sessionData before ready and wrote to localStorage from a hidden window. Local Storage, GPUCache, Cache, Code Cache, Network Persistent State and Preferences were all created in the session folder, and userData stayed empty. However, the helper processes still had --user-data-dir=<userData> on their command lines. So the manual check should not use "the mcp helpers no longer show the GUI's user-data-dir" as its pass criterion. That flag stays the same after this fix. The pass criterion has to be the behaviour: start Openscreen mcp, then the GUI, change the language, relaunch the GUI, and the prompt does not come back. You can also check that <userData>/Local Storage/leveldb/LOCK is held by the GUI (lsof), not by the mcp process.

Two gaps, if you want them:

1. CLI renderers now start with empty localStorage, so they lose GUI prefs they used to read. src/hooks/useScreenRecorder.ts:1233 sends loadUserPreferences().preferSoftwareEncoder to the Windows native helper. With this PR, openscreen record on Windows ignores a user's "prefer software encoder" choice. App.tsx also loads custom fonts from localStorage (src/lib/customFonts.ts). One way to keep read access without sharing the store: before setPath, copy the GUI's Local Storage into the new folder and skip LOCK:

   fs.cpSync(path.join(userData, "Local Storage"), path.join(own, "Local Storage"), {
   	recursive: true,
   	filter: (src) => path.basename(src) !== "LOCK",
   });

   Wrap it in try/catch, because the folder is absent on a fresh install. If a copy catches the store mid-write, Chromium discards and recreates that copy, and the GUI's own store is never touched.
2. Pid reuse: mkdirSync(own, { recursive: true }) on a folder left by a dead run with the same pid keeps that run's data. An rmSync(own, { recursive: true, force: true }) first gives every run a clean start. This is minor.

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Actionable comments posted: 4

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Inline comments:
Review comments at @electron/cli/sessionData.ts:
- Around line 44-47: Update the `own` directory setup in the session-data
initialization flow so a reused process PID cannot expose a prior run’s browser
state: assign each run a unique directory, or safely clear an existing PID
directory before setting `sessionData`. Preserve the existing stale-directory
cleanup behavior.
- Line 57: Make stale-session enumeration and cleanup best-effort around
staleCliSessionDirs: catch errors from readdirSync(root) or the sweep, log a
warning using the existing logger, and continue with the already assigned
isolated session instead of letting the error escape and abort CLI startup.
- Around line 23-25: Update the stale-session filtering around `isAlive` to
verify each directory’s recorded host and PID namespace match the current
process before using its PID for a liveness check or deletion; treat `ESRCH` as
evidence of exit only for a matching owner.
- Around line 32-35: Update the process liveness check’s catch block around
process.kill(pid, 0) so it returns false only when the error code is ESRCH;
treat EPERM and every other error as live or uncertain and keep the session
directory.

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📒 Files selected for processing (4)

• electron/cli/cliMain.ts
• electron/cli/sessionData.test.ts
• electron/cli/sessionData.ts
• electron/main.ts

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