[omartelo]

Summary

On the Pulls screen, Send on a pull request's "Comments for the session" batch typed the comments into whichever session was active before Pulls opened, with no check that it was working on that pull request's branch. The Files tab took inject/submit bound to the window's active session (main.go) and keyed the batch by that session's checkout.

• pullsScreen.reviewSession(d) picks where the pull request's comments go: a session in the checkout of its head branch, the active one when it sits there, the first otherwise. The window's active session in another checkout is never picked.
• With no session in that checkout, Send raises the existing "Open a session to send these comments to" and keeps the batch.
• A branch with no checkout keeps its batch under the pull request's URL; once Open in Session creates the checkout, commentStore.move carries the comments over, so nothing written before is lost.
• Line references injected from that tab follow the same rule.
• filesInput now carries the active session id and the injector/submitter factories instead of functions bound to the active session; sessionButton reads reviewSession.
• stale_pulls_test.go: the rig now wires sessionsIn and files the way main.go does (it used to rely on a nil guard the old hook had); no assertion changed.
• CHANGELOG.md [Unreleased] › Fixed entry.

Test plan

• native/: gofmt -l . clean, go vet ./... and go test ./... green
• TestPullRequestCommentsGoOnlyToASessionInItsBranchCheckout: branch checked out, active session inside and outside it, branch with no checkout
• TestCommentBatchMovesWholeAfterWhatItJoins: the batch moves after what the checkout already holds, an open edit follows it