fix(db): skip repeated passive before truncate

[corylanou]

Description

Persist a no-progress result from the emergency PASSIVE checkpoint attempt. While the logical WAL remains above the truncate threshold, later sync cycles go directly to TRUNCATE; the PASSIVE attempt is re-armed when the threshold clears or the WAL restarts.

This is intentionally limited to emergency checkpoint selection and its regression coverage. It is stacked on #1322 and targets issue-1310-disk-full-staging-wedge.

Motivation and Context

A pinned reader reproduced the issue: before the fix, two blocked sync cycles executed two PASSIVE checkpoints and two TRUNCATE checkpoints. After the fix, those same cycles execute one PASSIVE checkpoint and two TRUNCATE checkpoints, avoiding the repeated write-lock barrier, sequence bump, and bookkeeping L0 file while still attempting TRUNCATE every cycle.

The regression test also verifies that PASSIVE is retried after the truncate threshold clears and after the WAL restarts.

Fixes #1339

How Has This Been Tested?

• go test -race . -run 'TestDB_(SyncTruncateCheckpointFiresDuringChunkedCatchUp|CheckpointPassiveRestartSkipsTruncate|CheckpointTruncateSkipsRepeatedPassiveWithoutProgress)$' -count=5
• go test -race -v ./...
• pre-commit run --all-files
• go build -o bin/litestream ./cmd/litestream
• go build -o bin/litestream-test ./cmd/litestream-test
• All low-volume, high-volume, and burst-volume TestLTXBehavior soak profiles passed their behavioral, restore, and integrity checks.
• go test -tags 'integration,soak' -run '^TestLTXBehavior_NoExcessiveSnapshots$' -short -v -timeout 5m ./tests/integration/

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (would cause existing functionality to not work as expected)

Checklist

• My code follows the code style of this project (go fmt, go vet)
• I have tested my changes (go test ./...)
• I have updated the documentation accordingly (if needed)

[github-actions]

PR Build Metrics

✅ All clear — no issues detected

Check	Status	Summary
Binary size	✅	36.98 MB (0.0 KB / 0.00%)
Dependencies	✅	No changes
Vulnerabilities	✅	None detected
Go toolchain	✅	1.25.12 (latest)
Module graph	✅	1240 edges (0)

Binary Size

	Size	Change
Base (9566a1a)	36.98 MB
PR (7b3024d)	36.98 MB	0.0 KB (0.00%)

Dependency Changes

No dependency changes.

govulncheck Output

=== Symbol Results ===

No vulnerabilities found.

Your code is affected by 0 vulnerabilities.
This scan also found 0 vulnerabilities in packages you import and 1
vulnerability in modules you require, but your code doesn't appear to call these
vulnerabilities.
Use '-show verbose' for more details.

Build Info

Metric	Value
Build time	40s
Go version	go1.25.12
Commit	7b3024d

History (2 previous)

Commit	Updated	Status	Summary
71b259e	2026-07-16 15:08 UTC	✅	36.98 MB (0.0 KB / 0.00%)
722bbb8	2026-07-10 00:18 UTC	✅	36.98 MB (0.0 KB / 0.00%)

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_{🤖 Updated on each push.}