test(S01/T01): Added a job-scoped Gmail matching contract with backend-…

- JobTrackerApi/Controllers/GmailController.cs
- JobTrackerApi/Services/GmailOAuthService.cs
- JobTrackerApi.Tests/GmailControllerTests.cs
- .gsd/milestones/M001/slices/S01/S01-PLAN.md
- .gsd/KNOWLEDGE.md

.gsd/milestones/M001/slices/S01/tasks/T02-SUMMARY.md

@@ -0,0 +1,41 @@
+---
+title: T02 summary
+status: done
+files:
+  - Models/Correspondence.cs
+  - JobTrackerApi/Controllers/GmailController.cs
+  - JobTrackerApi/Controllers/CorrespondenceController.cs
+  - JobTrackerApi/Program.cs
+  - JobTrackerApi.Tests/GmailControllerTests.cs
+verification:
+  - $HOME/.dotnet/dotnet build JobTrackerApi/JobTrackerApi.csproj
+  - docker run --rm -v "$PWD":/src -w /src mcr.microsoft.com/dotnet/sdk:9.0 bash -lc '...dotnet test /tmp/gmailtests/GmailTests.csproj...'
+---
+
+Extended correspondence persistence and Gmail import continuity for S01.
+
+What changed:
+- `Models/Correspondence.cs`
+  - added `ExternalThreadId`
+  - added `ExternalFrom`
+  - added `ExternalTo`
+- `JobTrackerApi/Controllers/GmailController.cs`
+  - single-message import now returns `GmailImportMessageResultDto` with `Imported`, `Skipped`, `MessageId`, `ThreadId`, and the imported/existing `Correspondence`
+  - repeat single-message imports now report `Imported=0` / `Skipped=1` instead of returning a bare correspondence record
+  - imported Gmail messages now persist thread id plus raw sender/recipient metadata
+- `JobTrackerApi/Controllers/CorrespondenceController.cs`
+  - create request now accepts optional external message/thread/from/to metadata so the correspondence surface stays consistent with enriched imports
+- `JobTrackerApi/Program.cs`
+  - added SQLite compatibility guards for `Correspondences.ExternalThreadId`, `Correspondences.ExternalFrom`, and `Correspondences.ExternalTo`
+  - added MySQL compatibility guards for the same columns
+- `JobTrackerApi.Tests/GmailControllerTests.cs`
+  - added repeat single-message import coverage
+  - added repeat thread import coverage
+  - retained ranking and owned-job scope coverage from T01
+
+Verification:
+- Native API build passed with `$HOME/.dotnet/dotnet build JobTrackerApi/JobTrackerApi.csproj`
+- Isolated Gmail controller tests passed in Docker (`5 passed`)
+
+Important caveat:
+- The repository’s main `JobTrackerApi.Tests` project still has unrelated pre-existing compile failures outside Gmail tests, so the exact planned command `dotnet test JobTrackerApi.Tests/JobTrackerApi.Tests.csproj --filter GmailControllerTests` remains blocked by broader test drift. Gmail coverage itself passes when isolated.