# Task 2 Implementation Report

Date: 2026-09-03
Task: Build the Lock-Free Snapshot Coordinator
Worktree: `D:/workSpace/PROJECT_SPACE/FT546/FT546MWS/worktrees/shadow-from-main-20260811`

## What Changed

Implemented the JVM-local, observation-only snapshot coordinator using one immutable `AtomicReference<State>` and compare-and-set transitions.

- Added immutable `PublishedShadowSnapshot` metadata with generation, warehouse, synchronization time, and source signature.
- Added `ShadowSkipReason` values for startup, busy, stale, warehouse, and concurrent outcomes.
- Added `ShadowSnapshotCoordinator` with startup, ready, busy, and unavailable phases; bounded freshness checks; warehouse normalization through `WarehouseIdNormalizer.equivalent`; single observation leasing; refresh tickets; stamped publication; failure recovery state; and separately idempotent Legacy activity and observation-lease cleanup.
- Added behavior tests for startup, one lease, busy admission, exact-once cleanup, concurrent publication invalidation, comparability invalidation, stale snapshots, warehouse mismatch, numeric warehouse equivalence, and failed-refresh recovery.
- No gateway, SQL, cross-instance, or later-task behavior was added.

## Files Changed

- `ruoyi-admin/src/main/java/com/ruoyi/algorithm/shadow/PublishedShadowSnapshot.java`
- `ruoyi-admin/src/main/java/com/ruoyi/algorithm/shadow/ShadowSkipReason.java`
- `ruoyi-admin/src/main/java/com/ruoyi/algorithm/shadow/ShadowSnapshotCoordinator.java`
- `ruoyi-admin/src/test/java/com/ruoyi/algorithm/shadow/ShadowSnapshotCoordinatorTest.java`

## TDD Evidence

### RED

The initial direct reactor command could not resolve locally built reactor dependencies:

```text
D:/BDevTools/maven/apache-maven-3.9.11/bin/mvn.cmd -pl ruoyi-admin -Dtest=ShadowSnapshotCoordinatorTest test
```

It failed before compilation with missing `ruoyi-framework`, `ruoyi-quartz`, `ruoyi-generator`, and `fortucky-algorithm` artifacts. Following the brief, the same named test scope was rerun with the reactor fallback:

```text
D:/BDevTools/maven/apache-maven-3.9.11/bin/mvn.cmd -pl ruoyi-admin -am -Dtest=ShadowSnapshotCoordinatorTest -Dsurefire.failIfNoSpecifiedTests=false test
```

Expected RED output:

```text
[ERROR] ...ShadowSnapshotCoordinatorTest.java:[108,13] cannot find symbol
  symbol:   class ShadowSnapshotCoordinator
[ERROR] ...ShadowSnapshotCoordinatorTest.java:[112,20] cannot find symbol
  symbol:   class PublishedShadowSnapshot
[ERROR] ...ShadowSnapshotCoordinatorTest.java:[116,33] cannot find symbol
  symbol:   class ShadowSnapshotCoordinator
[ERROR] ...ShadowSnapshotCoordinatorTest.java:[116,72] cannot find symbol
  symbol:   class PublishedShadowSnapshot
[INFO] ruoyi-admin ........................................ FAILURE
[INFO] BUILD FAILURE
```

The failure was the intended missing-production-type compilation failure; no test behavior ran before implementation.

### GREEN

After the minimum production implementation, the focused command was run twice:

```text
D:/BDevTools/maven/apache-maven-3.9.11/bin/mvn.cmd -pl ruoyi-admin -am -Dtest=ShadowSnapshotCoordinatorTest -Dsurefire.failIfNoSpecifiedTests=false test
```

Run 1:

```text
[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0
[INFO] ruoyi-admin ........................................ SUCCESS
[INFO] BUILD SUCCESS
```

Run 2:

```text
[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0
[INFO] ruoyi-admin ........................................ SUCCESS
[INFO] BUILD SUCCESS
```

Both runs completed without timing sleeps.

## Full-Suite Evidence

Before committing, the relevant reactor suite was run once:

```text
D:/BDevTools/maven/apache-maven-3.9.11/bin/mvn.cmd -pl ruoyi-admin -am -Dsurefire.failIfNoSpecifiedTests=false test
```

Result:

```text
fortucky-algorithm: Tests run: 122, Failures: 0, Errors: 0, Skipped: 0
ruoyi-admin:        Tests run:  26, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS
```

Total: 148 tests, 0 failures, 0 errors, 0 skipped. The output included existing Lombok equals/hashCode and deprecation warnings in unrelated sources; none were introduced by this task.

## Self-Review

- Confirmed the staged change contained exactly the four brief-listed implementation/test files.
- `git diff --cached --check` completed cleanly.
- Confirmed the coordinator has one `AtomicReference<State>` and CAS loops for admission, exit, lease cleanup, refresh begin, publication, and refresh failure.
- Confirmed `exit` and `finishObservation` use separate per-admission `AtomicBoolean` guards.
- Confirmed caller admission performs only bounded in-memory work and atomic transitions; there is no synchronized block, lock, wait, sleep, database call, gateway call, or SQL behavior.
- Confirmed the publication CAS uses the refresh ticket's full stamped `State` object, so activity or any intervening state replacement invalidates publication even when generation values match.
- Confirmed numeric warehouse equivalence delegates to the Task 1 normalizer and freshness defaults to 60 seconds.
- No subagents or external reviewers were dispatched, per request.

## Commit

`c6a8b4f feat: coordinate stable shadow snapshots`

## Concerns

- The coordinator intentionally does not wait for the configured quiet interval; it records `quietSince`, while the later background worker owns waiting and refresh scheduling.
- Gateway integration, SQL refresh/publication, metrics, and cross-instance coordination remain later tasks by design.
- The report is a standalone delivery artifact at the requested path; the feature commit contains the four files listed in the brief.

## Fix Round 1

- Changed `ShadowSnapshotCoordinator` to accept an injectable `java.time.Clock`; `exit` now records `clock.instant()` instead of `Instant.now()`.
- Added tests proving stale/warehouse skips transition to `BUSY` and recover via refresh, plus deterministic quiet-since timing.
- RED: focused reactor command initially failed in this shell because `mvn` resolved an incompatible Maven/plugin environment; the corrected Maven 3.9.11 command then compiled and exercised the new tests.
- GREEN: `D:/BDevTools/maven/apache-maven-3.9.11/bin/mvn.cmd -pl ruoyi-admin -am -Dtest=ShadowSnapshotCoordinatorTest '-Dsurefire.failIfNoSpecifiedTests=false' test` passed twice; 7 tests, 0 failures, 0 errors each run.
- Commit: pending.
- Concerns: default constructors retain `Clock.systemUTC()` behavior; no gateway, SQL, or Legacy behavior changed.