fix(session-broker): detect Windows bunfs paths when auto-launching the daemon

[benvinegar]

Fixes #502.

What

On Windows, Bun-compiled single-file executables report argv[1] as a virtual path on Bun's B: drive (B:\~BUN\root\hunk.exe — the reporter's log shows the forward-slash form). resolveDaemonLaunchCommand only recognized the Unix virtual prefix (/$bunfs/), so the Windows path fell through to the script-entrypoint branch (it contains path separators) and the auto-launched daemon became hunk.exe B:/~BUN/root/hunk.exe daemon serve — the compiled binary received the virtual path as a bogus first argument, the daemon never started, and hunk session list found no sessions unless hunk daemon serve was started manually.

How

Recognize the Windows bunfs prefix (b:/~bun/, case-insensitive, either separator) alongside /$bunfs/ in a small isBunfsEntrypoint helper, so compiled binaries relaunch via execPath with clean daemon serve args on every platform.

Testing

• New unit test covering both separator forms; verified it fails against the previous implementation and passes with the fix.
• bun run typecheck, full bun test (1084 pass), format, lint.
• Not verified on real Windows hardware — the repro in Windows: hunk diff auto-launches daemon with invalid Bun argv #502 maps exactly onto the argv shapes covered by the unit test, but a confirmation from the reporter after release would be good.

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR fixes a Windows-only bug where Bun single-file executables reported argv[1] as a virtual B:/~BUN/... path instead of the Unix /$bunfs/... prefix, causing the daemon auto-launch to pass that virtual path as a bogus argument and silently fail.

• Introduces a small isBunfsEntrypoint helper that recognises both the Unix (/$bunfs/) and Windows (b:/~bun/, case-insensitive, either separator) virtual-path prefixes, replacing a direct startsWith call in resolveDaemonLaunchCommand.
• Adds a targeted unit test covering both separator forms (B:/~BUN/... and B:\\~BUN\\...) for the Windows branch, alongside the changeset note.

Confidence Score: 5/5

Safe to merge — the change is a narrow, well-tested detection fix with no impact on non-Windows paths.

The fix is minimal and surgical: one new helper function with two branches (existing Unix prefix unchanged, new Windows prefix added), a module-level constant, and an updated call site. Both separator forms for the Windows virtual path are covered by the new test. No existing behavior changes on Unix or native-binary paths, and the SCRIPT_ENTRYPOINT_PATTERN fallback is unaffected.

No files require special attention.

Important Files Changed

Filename	Overview
src/session-broker/brokerLauncher.ts	Adds isBunfsEntrypoint helper and BUNFS_WINDOWS_PREFIX constant; replaces inline startsWith with the new helper in resolveDaemonLaunchCommand. Logic is correct and well-commented.
src/session-broker/brokerLauncher.test.ts	New test covers Windows bunfs paths with both forward-slash and backslash separators; uses a realistic Windows binary path as execPath. Good coverage of the new branch.
.changeset/windows-bunfs-daemon-argv.md	Adds a patch-level changeset entry for hunkdiff describing the Windows daemon auto-launch fix.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["resolveDaemonLaunchCommand(argv, execPath)"] --> B{"argv[1] exists?"}
    B -- No --> E["return { command: execPath, args: ['daemon','serve'] }"]
    B -- Yes --> C{"isBunfsEntrypoint(argv[1])?"}
    C -- "starts with /$bunfs/ (Unix)" --> D["return { command: execPath, args: ['daemon','serve'] }"]
    C -- "matches b:/~bun/ after normalize (Windows)" --> D
    C -- No --> F{"SCRIPT_ENTRYPOINT_PATTERN matches?"}
    F -- Yes --> G["return { command: execPath, args: [argv[1],'daemon','serve'] }"]
    F -- No --> E

    style D fill:#22c55e,color:#fff
    style G fill:#3b82f6,color:#fff
    style E fill:#3b82f6,color:#fff

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flowchart TD
    A["resolveDaemonLaunchCommand(argv, execPath)"] --> B{"argv[1] exists?"}
    B -- No --> E["return { command: execPath, args: ['daemon','serve'] }"]
    B -- Yes --> C{"isBunfsEntrypoint(argv[1])?"}
    C -- "starts with /$bunfs/ (Unix)" --> D["return { command: execPath, args: ['daemon','serve'] }"]
    C -- "matches b:/~bun/ after normalize (Windows)" --> D
    C -- No --> F{"SCRIPT_ENTRYPOINT_PATTERN matches?"}
    F -- Yes --> G["return { command: execPath, args: [argv[1],'daemon','serve'] }"]
    F -- No --> E

    style D fill:#22c55e,color:#fff
    style G fill:#3b82f6,color:#fff
    style E fill:#3b82f6,color:#fff

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