the-other-dude/.planning/phases/05-diff-engine/05-01-SUMMARY.md

phase, plan, subsystem, tags, requires, provides, affects, tech-stack, key-files, key-decisions, patterns-established, requirements-completed, duration, completed

phase	plan	subsystem	tags	requires	provides	affects	tech-stack	key-files	key-decisions	patterns-established	requirements-completed	duration	completed
05-diff-engine	01	api	difflib unified-diff openbao transit prometheus nats	phase provides 03-snapshot-ingestion config snapshot subscriber and router_config_snapshots table phase provides 01-database-schema router_config_diffs table schema	generate_and_store_diff() for unified diff between consecutive snapshots Prometheus metrics for diff generation success/failure/timing Subscriber integration calling diff after snapshot INSERT	06-change-parser 07-timeline-api	added patterns difflib best-effort-secondary-operation tdd-red-green	created modified backend/app/services/config_diff_service.py backend/tests/test_config_diff_service.py backend/app/services/config_snapshot_subscriber.py backend/tests/test_config_snapshot_subscriber.py	Diff service instantiates its own OpenBaoTransitService per-call with close() for clean lifecycle RETURNING id added to snapshot INSERT to capture new_snapshot_id for diff generation Subscriber tests mock generate_and_store_diff to isolate snapshot logic from diff logic	Best-effort secondary operations: wrap in try/except, log+count errors, never block primary flow Line counting excludes unified diff headers (+++ and --- lines)	DIFF-01 DIFF-02	3min	2026-03-13

Phase 5 Plan 1: Config Diff Service Summary

Unified diff generation between consecutive config snapshots using difflib with Transit decrypt and best-effort error handling

Performance

• Duration: 3 min
• Started: 2026-03-13T03:30:07Z
• Completed: 2026-03-13T03:33:Z
• Tasks: 2
• Files modified: 4

Accomplishments

• Config diff service generates unified diffs between consecutive snapshots per device
• Transit decrypt of both old and new ciphertext before diffing in memory
• Best-effort pattern: decrypt/DB failures logged and counted, never block snapshot ack
• Prometheus metrics track diff success, errors (by type), and generation duration
• Subscriber wired to call diff generation after every successful snapshot INSERT

Task Commits

Each task was committed atomically:

1. Task 1: Diff generation service (TDD RED) - 79453fa (test)
2. Task 1: Diff generation service (TDD GREEN) - 72d0ae2 (feat)
3. Task 2: Wire diff into subscriber - eb76343 (feat)

TDD task had separate RED and GREEN commits

Files Created/Modified

• backend/app/services/config_diff_service.py - Diff generation with Transit decrypt, difflib, Prometheus metrics
• backend/tests/test_config_diff_service.py - 5 unit tests covering diff, first-snapshot, decrypt failure, line counts, empty diff
• backend/app/services/config_snapshot_subscriber.py - Added RETURNING id, generate_and_store_diff call after commit
• backend/tests/test_config_snapshot_subscriber.py - Updated to mock generate_and_store_diff

Decisions Made

• Diff service instantiates its own OpenBaoTransitService per-call (clean lifecycle, consistent with subscriber pattern)
• RETURNING id added to snapshot INSERT SQL to capture the new_snapshot_id without a separate query
• Subscriber tests mock generate_and_store_diff to keep snapshot tests isolated and unchanged in assertion counts

Deviations from Plan

Auto-fixed Issues

1. [Rule 1 - Bug] Updated subscriber test assertions for diff integration

• Found during: Task 2 (wire diff into subscriber)
• Issue: Existing subscriber tests failed because generate_and_store_diff made additional DB calls through the shared mock session
• Fix: Added patch for generate_and_store_diff in subscriber tests that successfully INSERT (test 1 and test 6)
• Files modified: backend/tests/test_config_snapshot_subscriber.py
• Verification: All 11 tests pass
• Committed in: eb76343 (Task 2 commit)

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Total deviations: 1 auto-fixed (1 bug) Impact on plan: Necessary to maintain test isolation. No scope creep.

Issues Encountered

None

User Setup Required

None - no external service configuration required.

Next Phase Readiness

• Diff generation is active and will produce diffs for every new non-duplicate snapshot
• router_config_diffs table populated with diff_text, line counts, and snapshot references
• Ready for change parser (Phase 6) to parse semantic changes from diff_text

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Phase: 05-diff-engine Completed: 2026-03-13