[BUG] Cowork: claude://cowork/new?q= prompt renders but doesn't commit when app already running — no Send button, placeholder still shown (fresh launch works)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

⚠️ Not a duplicate — each candidate read in full: - #64879 — session reuse: a second deeplink's attachments land in the prior deeplink's session. This report is about the q= prompt text never committing to composer state (no Send button); reproduces even on the very first deeplink of an app run. - #53402 — folder carryover into new sessions (closed/fixed). Same fresh-launch-vs-running dichotomy, different defect — nothing here involves inherited folders. - #10662 — claude.ai web interface: Send button disabled after attaching a GitHub repository. Different surface, different trigger; here the Send button never appears because the deeplink prefill isn't registered as input. - #61718 / #66310 — queued messages not firing mid-conversation (Queue button flows). No queue involved here; the composer is pre-first-message and the prompt never becomes sendable. - #57887 / #19023 — closed feature requests asking for prompt-prefill deep links. This is a bug in the since-shipped claude://cowork/new?q= behavior documented at code.claude.com/docs/en/deep-links.

Summary

When Claude Desktop is already running, firing a claude://cowork/new?q=<prompt>&folder=<path> deeplink renders the q= prompt text in the Cowork composer but never commits it to the composer's input state:

• The prompt text is painted overlapping the "How can I help you today?" placeholder (both visible at once).
• No Send button appears — the composer behaves as if empty.
• Typing any character (e.g. a single space) commits the text: the placeholder clears and Send appears with the full prompt intact.

The same URL works correctly on a fresh app launch (quit Claude fully, then open the link): the prompt is committed, placeholder cleared, Send button present.

Ruled out (all fail identically when the app is already running, on the current build):

• Parameter order (q= first vs folder= first)
• Folder location (inside vs outside ~/Documents/Claude/Projects/)
• Folder contents (empty vs containing CLAUDE.md/files)
• Folder permission state (first-time trust dialog vs "You've allowed this folder before" dialog — bug reproduces through both dialog variants)
• Omitting folder= entirely (q=-only also fails)

Why this matters

The documented use case for these links is "Open in Cowork" buttons in third-party tools and artifacts (docs: "the prompt is populated but not sent until you press Enter"). A user clicking such a button inside a Cowork artifact by definition has the app already open, so the broken path is the only path for that flow — every real-world click hits it. Non-technical users see a dead composer and conclude the product is broken; they don't discover the type-a-character workaround.

Regression note

Behavior degraded across an auto-update mid-day on 2026-07-02: on the prior build, deeplinks pointing at never-before-attached folders committed the prompt correctly while the app was running (verified working 3/3 that morning); after updating to 1.18286.0 the same URLs fail. Exact prior version unknown (auto-update). Artifact-launched deeplinks were also verified fully working on 2026-06-30.

What Should Happen?

Firing claude://cowork/new?q=<prompt> while the app is running should behave exactly like the fresh-launch case: prompt committed to the composer (placeholder cleared), Send button active, prompt sendable with a single Enter/click.

Error Messages/Logs

Steps to Reproduce

1. Launch Claude Desktop and leave it on the Cowork home screen ("Let's knock something off your list").
2. From a browser or terminal, open: claude://cowork/new?q=Hello%20world&folder=%2FUsers%2Fme%2Fsome-folder (any absolute folder path).
3. Approve the folder-attach confirmation dialog.
4. Actual: composer shows "Hello world" rendered over the still-visible "How can I help you today?" placeholder; no Send button; pressing Enter does nothing. Typing one character commits the text and Send appears.
5. Quit Claude fully (⌘Q). Open the same URL again.
6. Expected (and actual on fresh launch): prompt committed, placeholder cleared, Send button present.

Claude Model

None

Is this a regression?

Yes

Last Working Version

Unknown (desktop auto-update); partially working on the prior build the same day — see regression note

Claude Code Version

Claude Desktop 1.18286.0

Platform

Anthropic API

Operating System

macOS 15.5 (24F74)

Additional Information

Reproduced across two app builds (pre- and post-update on 2026-07-02) and ~12 URL/folder/dialog permutations. Happy to provide screenshots or a screen recording.