fix(checkpoint): honor cancellation and show progress in push + import loops

[gtrrz-victor]

https://entire.io/gh/entireio/cli/trails/993

Summary

The git-refs checkpoint push drain and the agent-history import loop each iterate an unbounded, user-scaled collection (checkpoint refs / imported sessions) doing per-item work, but never observed context cancellation and gave no per-item progress. Surfaced while looking into auto-import on entire enable:

1. No progress during the per-ref divergence push — just a spinner, so the user couldn't tell how much was left.
2. Context cancel not propagated into the push loop — Ctrl-C during the user's git push was ignored.
3. Unbounded work — many sessions/refs could keep the loop running for a long time with no way to stop.

What Changed

flushCheckpointRefsQueue (strategy/manual_commit_push.go)

• Per-ref k/N progress counter in the divergence recovery loop (was a single spinner over the whole loop).
• Cancellation short-circuit right after the batch push fails — a cancelled batch is not a divergence, so we bail cleanly instead of entering per-ref recovery.
• ctx.Err() break inside the per-ref loop for a cancel that lands mid-recovery.
• Only confirmed-pushed refs leave the queue, so the remainder is retried on the next push (no queue corruption, no force-push).

agentimport.Run (agentimport/agentimport.go)

• ctx.Err() check at the top of the session loop so a large import stops cleanly between sessions. Already-written checkpoints stay put (idempotent by deterministic ID), so a re-run resumes where it left off.

runSelectedImports (setup_import.go) — from PR review

• Treats context.Canceled from agentimport.Run as an abort of the whole enable auto-import phase: prints a single Import cancelled. note and returns, instead of continuing to the next agent (which would re-run Discover and emit another "context canceled" note per remaining agent).

Reaction to cancel is uniform: stop, keep only what actually landed, leave the rest for a retry, surface context.Canceled. Callers already handle it (pre-push logs and never blocks the user's push; doctor_migrate exits silently via errors.Is).

Deferred (not in this PR)

Issue 3's structural fix — parsing git push --porcelain output so a single diverged ref among thousands triggers one recovery instead of demoting the whole batch to per-ref recovery. Discussed but intentionally left for a follow-up.

Verification

• go test ./cmd/entire/cli/agentimport/... ./cmd/entire/cli/strategy/... ./cmd/entire/cli/ — pass (incl. after merging main).
• Regression tests: TestFlushCheckpointRefsQueue_CancelledContextStopsCleanly (push), TestRun_CancelledContextStopsBeforeScanning (import), TestRunSelectedImports_CancelStopsImportPhase (enable phase abort — asserts the second agent is never processed).
• golangci-lint run on the touched packages — 0 issues. gofmt clean.
• Merged latest main and resolved the manual_commit_push.go conflict (adopted main's reworded, cause-agnostic failure message and dest.target push-destination refactor while keeping the per-ref progress + cancellation handling).

[Copilot]

Pull request overview

Improves long-running checkpoint-related loops (git-refs push drain and agent transcript import) by honoring context cancellation and surfacing clearer per-item progress, so users can reliably interrupt large operations and understand forward progress during divergence recovery.

Changes:

• Add cancellation short-circuits and in-loop ctx.Err() checks to stop cleanly on Ctrl-C while preserving retry semantics.
• Improve stderr progress output during per-ref divergence recovery with k/N counters and per-ref spinners plus a final synced summary.
• Add regression tests covering pre-cancelled contexts for both the push drain and import loop.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
cmd/entire/cli/strategy/manual_commit_push.go	Adds cancellation handling and clearer per-ref progress output in flushCheckpointRefsQueue divergence recovery.
cmd/entire/cli/strategy/refs_push_test.go	Adds a regression test ensuring cancelled contexts stop cleanly and leave refs queued/unpushed.
cmd/entire/cli/agentimport/agentimport.go	Adds a ctx.Err() guard at the top of the per-session loop to stop imports cleanly between sessions.
cmd/entire/cli/agentimport/agentimport_test.go	Adds a regression test verifying cancelled imports do not scan sessions or write checkpoints.

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[gtrrz-victor]

Duplicated -> #1925