fix(task-input): prefill repo dropdown when starting task from sidebar "+" icon

[mp-hog]

Problem

Closes #1454

In the Tasks sidebar each repo group header has a hover "+" button to start a new task. Clicking it did not scope the new-task screen with that repo in cloud-mode, so that tasks were started under wrong repo.

It's this relation:

Fix

Make folderId drive both selectors. A registered folder already carries both path (local) and remoteUrl (the resolved owner/repo slug), so it's a single source of truth.

New useInitialRepoSelectionFromFolderId hook + pure resolveRepoSelectionForFolder resolver:

• always prefill the local directory from the folder path
• prefill the cloud repo when the folder's remote is a real owner/repo that is a connected GitHub integration
• keep the current workspace mode when it can represent the repo, and only switch (Cloud → last-used local mode) when it can't (a local-only repo while in Cloud). The switch uses the non-persisting setter, so it doesn't overwrite the user's mode preference.

Behavior

You're in	Click "+" on…	Result
Cloud	cloud-capable repo	dropdown follows the repo; stay in Cloud
Local	dual-capable repo	directory prefilled; stay in Local (cloud repo also seeded)
Cloud	local-only repo	switch to Local; directory prefilled
—	generic New task button	unchanged — falls to last-used defaults

Testing

• Unit tests for the pure resolver, areReposReady, and the hook cover every branch incl. the loading-gate and once-per-folderId guard.
• @posthog/ui typecheck + biome clean; task-detail suite green (22/22); full @posthog/ui suite green (752/752).
• Manually with local app, + icon switches to respective repo

Known limits (out of scope)

• A cloud-only group with no registered local folder falls back to defaults (no folderId/remoteUrl to key off).
• In Cloud mode, "+" on a repo whose org is not a connected GitHub integration intentionally switches to Local (per the "switch only when the mode can't represent the repo" rule).

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 1cf21bb.}

[greptile-apps]

Prompt To Fix All With AI

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 2
packages/ui/src/features/task-detail/hooks/useInitialRepoSelectionFromFolderId.test.ts:241-267
**Missing "waits for folders to load" test case**

The deleted `useInitialDirectoryFromFolderId.test.ts` explicitly tested the scenario where `folders` starts empty and the target folder arrives in a later render. That case is absent from the new test file. The hook bails early when `folders.find()` returns `undefined` and intentionally leaves `dirInitRef.current` unset so the effect retries once `folders` loads — but without a test for this path, a future regression (e.g., accidentally setting `dirInitRef.current` before finding the folder) would go unnoticed.

### Issue 2 of 2
packages/ui/src/features/task-detail/hooks/useInitialRepoSelectionFromFolderId.ts:22-29
**`areReposReady` permanently returns `false` when integration exists but repos are empty**

When `hasGithubIntegration = true` and `repositoriesCount = 0` is not a transient gap (e.g., a user installed the GitHub App then revoked access to every repository), `areReposReady` never returns `true`. As a result `reposLoaded` stays `false` in the hook, `repoModeInitRef.current` is never set, and clicking "+" on a local-only folder while in Cloud mode silently leaves the user in Cloud mode. The directory prefill still fires, so the failure is partial rather than total — but the mode switch the fix promises never happens for this cohort.

_{Reviews (1): Last reviewed commit: "fix(task-input): distinguish settled-emp..." | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "Merge branch 'main' into posthog-code/pr..." | Re-trigger Greptile}

[charlesvien]

Hey @mp-hog, how should this work if I am working on a local task, I click "+"? I would expect this to pre-fill the repo on local, but right now it does not and always tries to find the cloud repo.

[mp-hog]

Hey @mp-hog, how should this work if I am working on a local task, I click "+"? I would expect this to pre-fill the repo on local, but right now it does not and always tries to find the cloud repo.

Thanks for your feedback @charlesvien !

Before this PR the open mode is the global last-used setting (which does not distinguish between repo). The logic for this PR the same logic, but it adds a fallback to Local if the mode is not applicable under the given repo (it wouldn't switch to Cloud).

You are right though that it might still be surprising, as we don't distinguish this setting between repos, but the PR as is improves the Repo-Selection and is not making the Mode selection worse.

I have locally started working on infering the Mode from the task history of a repo, but it touches a bunch of files and I think goes beyond the scope of this PR. That I believe would solve the surprising bit of the current logic.

I would suggest: Ship as is and improve the Mode-selection in a follow-up. What do you think?

Edit: Follow-up: #2939