feat(browser): spin up browser cells from the command center

[MattPua]

Problem

Stacked on #3181. The command center can spin up tasks and terminals in grid cells, but not the new browser — you should be able to drop a browser next to a running task the same way.

Changes

CleanShot.2026-07-06.at.13.14.47.mp4

• Browser option in the empty-cell picker, next to Terminal and Brainrot (same posthog-code-browser-tab flag)
• Cells encode as __browser__:<url> (mirrors __terminal__:<id>) so the page restores on app reload
• BrowserCell reuses BrowserPanel from feat(browser): in-app browser tab with webview security hardening #3181; header shows the page title, falling back to the url hostname
• updateBrowserCellUrl is guarded so a stale debounced navigation callback can't clobber a cell that was reassigned

No new security surface: the webview and all main-process guards are the ones shipped in #3181.

How did you test this?

• Grid helper round-trip tests (incl. urls containing the prefix delimiter, empty-string cells)
• command-center + browser suites pass (125 tests), typecheck + biome clean

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 65282d9.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "feat(browser): spin up browser cells fro..." | Re-trigger Greptile}

[greptile-apps]

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[github-actions]

Clean additive feature: browser cell type wired up alongside the existing terminal/task/brainrot cells using the same prefix-encoding pattern. Core logic stays in @posthog/core, UI in @posthog/ui, store actions are correctly guarded, and the one resolved inline bot comment was a minor useCallback style concern with no correctness impact on native buttons.

New commits pushed (delta classified non_linear_history) — stamphog approval dismissed; re-review running automatically.

[github-actions]

Clean additive feature following the established prefix-encoding pattern for cell types. Core logic stays in @posthog/core, UI in @posthog/ui, store guards are correct (bounds check in setBrowserCell, type guard in updateBrowserCellUrl), the null vs falsy distinction for empty-string URLs is handled properly, and the tests cover the tricky delimiter-in-URL edge case.