plat 249

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PLAT-249 — auto browser mode omits the built-in host Downloads grant

Coordination	Value
Assigned agent	Unassigned
Ticket state	fixed
Last synchronized	2026-08-29

• Priority: filesystem capability, severity medium.
• Evidence: The jobsearch manifest used browser_mode: "auto" with CDP port 9222, but its live shell guard omitted /Users/mipl/Downloads entirely. The agent then incorrectly substituted legacy workspace Downloads/.

Problem

Three wiring gaps removed the intended grant from the main Builder session. The host Downloads helper accepted only the literal mode cdp; manifests commonly store browser_mode: "auto" with a configured CDP port, but the resolver returned auto before checking that port. In addition, the main Workflow Builder initialized its Folder Guard without calling the host Downloads grant helper even though child/background workshop sessions did call it. Finally, the coding-agent conversation restore path rebuilt the guard independently and passed raw auto to the CDP-only helper, so restarting and continuing the same Builder conversation still lost the exception.

The failed command targeted workspace-docs/Downloads, which is a different, legacy/general-chat staging folder. Workflow runs use their run-scoped execution/Downloads; host Downloads is a deliberate CDP-only exception.

Resolution

The host Downloads mode resolver now treats auto as unresolved intent. When a CDP port is configured it resolves to cdp, causing the existing session helper to add the user's host Downloads directory to both ReadPaths and WritePaths. The main Builder now applies the same helper as its child sessions, and the normal/restored coding-agent server paths resolve browser intent before calling it.

Workflow Builder sessions do not receive root workspace-docs/Downloads access. Workflow-generated files stay in the workflow or its run-scoped execution/Downloads. By owner decision, CDP-enabled workflows now receive read-write access to the host Downloads directory by default so shell and browser automation can stage and retrieve the same files. Non-browser and headless workflows receive no such host grant.

Verification

• A focused regression test reproduces browser_mode: "auto" plus CDP port 9222, requires it to resolve to cdp, and verifies the resulting Builder guard contains the host path in both reads and writes with no stale write denial.
• Server-mode coverage requires restored auto sessions with configured CDP candidates to resolve the host Downloads exception to cdp, while headless sessions remain headless.
• A companion test proves auto without a CDP port does not broaden access.
• Focused workflow-agent tests pass.