feat(code): warn on local task branch mismatch

[adboio]

Problem

we want task isolation, but we can only do so much with local tasks, since they are simply not in an isolated environment

downstack #1594 + #1595 add automatic branch linking to tasks, so when an agent touches a file, or an agent/human creates a branch from posthog code, we associate that branch to that task

now, we need a way to keep the user in the loop on what's happening, and steer them in the right direction

Changes

adds a UI warning if you send a prompt in a task that has a linked branch, but that branch is not currently checked out

details:

• hooks into tiptap with a new onBeforeSendso prompt is never lost if you cancel
• the warning is "blocking" in the sense that you have to make a decision. you can:
  • "continue anyway" -> ignore the warning, agent works in your current branch
    • automatic branch linking will still occur and maybe overwrite the current link, per the standard rules (see feat(code): enable branch linking for local tasks #1595 )
  • "switch branch" - checks out the task's linked branch
    • warns if there are uncommitted changes on current branch. this does not block, and surfaces errors from the switch (if any) in the dialog

How did you test this?

manually

[adboio]

• feat(code): warn on local task branch mismatch #1596 👈 (View in Graphite)
• feat(code): enable branch linking for local tasks #1595
• feat(code): add linked branch db model #1594
• main

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