fix(browser): Canvas navigation times out after preview_open returns an empty invisible tab #6

Problem

The agent cannot open Canvas in T3's shared browser, blocking access to an existing conversation/research board. The user reports Canvas now works for them, but a fresh agent retry still failed. This does not establish that Canvas itself is down.

Target origin: https://canvas.scaleadvertisement.com/

Related browser investigations: #1 and #4. This issue tracks the current navigation/readiness failure separately from account continuity and input/popup work.

Observed behavior

Reproduced during a fresh retry on 29 October 2026:

1. preview_status({}) returned no active tab (available: false). The persistent default profile was listed.
2. preview_open({url: <Canvas board URL>, profileId: "default", reuseExistingTab: false, open: true}) took about 15 seconds and returned a new agent-owned Default-profile tab, but with url: "", title: null, loading: false, and visible: false. No explicit failure was reported.
3. preview_snapshot({tabId: <new tab>, includeImage: false}) returned:

   Preview snapshot failed: Preview automation snapshot timed out after 15000ms.
   

4. Navigating that same tab to the Canvas origin, using readiness: "domContentLoaded" and timeoutMs: 15000, returned:

   Preview automation navigate timed out after 15000ms.
   

An earlier attempt in this conversation produced the same failures. Its subsequent status showed an empty URL, a title beginning Loading https://canvas.scaleadvertisement.com/, and loading: true.

The fallback computer-use in-app browser independently returned:

The browser access host is unavailable

Treat that fallback-host error as a separate observation until evidence connects it to T3's timeout. T3 successfully opened and inspected Instagram earlier in this conversation; that was not repeated as a control after the latest failure.

Reproduce and diagnose

• Inspect the actual current T3 desktop/server builds, browser runtime host, active persistent profile, and relevant logs. Exact build versions were not captured in this retry; do not assume versions from older issues still apply.
• Use T3's shared preview tools and explicitly select profileId: "default". Test the Canvas origin, then a board accessible to the authorized account.
• Compare with a neutral control page in a separate task-owned tab to distinguish a site-specific navigation problem from a browser transport/readiness failure.
• Determine whether navigation is blocked by browser-host connectivity, name resolution/network/TLS, the target response, page readiness, authentication/redirect handling, or the automation transport. These are investigation paths, not established causes.
• Inspect why preview_open reports an available tab with empty URL, loading: false, and no explicit navigation error after the wait, despite open: true and visible: false.
• Keep the user's report that Canvas works separate from automated proof of board access. Preserve existing authenticated sessions and board content.

Expected result and acceptance

• Opening a reachable site either produces an accurately reported ready/loading tab or a concrete navigation failure, rather than a misleading success-shaped response.
• The requested preview is visible, or its inability to become visible is explicitly reported.
• T3 can open an authorized Canvas board and read meaningful board content with preview_snapshot.
• Verify the actual board route after any fix. An origin response or HTTP 200 alone is insufficient.
• Record the root cause, changed components, running build/environment, and focused verification. Explain whether the separate in-app browser host error remains unresolved.

No fix, deployment, restart, profile reset, or board modification was performed during this reporting task.