Add project-context.md for sourcedb-to-spanner

[aasthabharill]

b/521647942

[gemini-code-assist]

Summary of Changes

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This pull request introduces documentation and architectural diagrams for the sourcedb-to-spanner Dataflow template. The addition of a project context file and visual architecture mapping aims to improve onboarding and provide a clear reference for the pipeline's design, technical stack, and operational procedures.

Highlights

• Project Documentation: Added a comprehensive project-context.md file to provide developers and AI agents with essential information about the sourcedb-to-spanner pipeline.
• Architecture Visualization: Included an architecture diagram in both .dot and .svg formats to visually represent the data flow and component structure of the migration pipeline.

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[gemini-code-assist]

Code Review

This pull request adds architecture documentation for the sourcedb-to-spanner pipeline, including a Graphviz DOT file, its SVG rendering, and a comprehensive project context markdown file (project-context.md). The review feedback recommends correcting a hardcoded local user directory path to a relative path, and resolving inconsistent project variable names (PROJECT vs PROJECT_ID) alongside replacing hardcoded testing resources with generic placeholders in the build and run commands.

[VardhanThigle]

Looks good. Thanks for the change request. A few open points for discussion.

[manitgupta]

How is this different from a README?

…

On Tue, 9 Jun 2026 at 12:14 PM, Vardhan Vinay Thigle < ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In v2/sourcedb-to-spanner/project-context.md <#3899 (comment)> : > + * [CS Reader for Bulk Migration](http://go/cs-reader-for-bulk-migration-to-spanner) - Reader design. + * [Spanner Bulk Migration User Guide](http://go/spanner-bulk-migration-user-guide) - Usage instructions. +* **Architecture Diagram:** [architecture.svg](architecture.svg) + +## AI Agent Tips + +* **Common Tasks:** Adding new JDBC dialects, fixing parsing errors, implementing new transformations or schema overrides, adding new source reader capabilities. +* **Coding Standards & Best Practices:** + * Use `AutoValue` for POJOs. + * Strict adherence to Apache Beam paradigms (PTransforms, DoFns). Use `TupleTag` for side outputs like the DLQ. + * Use structured logging (`com.google.cloud.teleport.structured-logging`). +* **Testing Frameworks & Guidelines:** + * **Frameworks:** JUnit 4, Google Truth for assertions, Mockito for mocking. + * **Rules:** Ensure tests use ***@***.***(JUnit4.class)`. Use embedded databases for testing when possible (e.g. `derby` or `embedded-cassandra`). +* **Areas to be Careful:** Cross-shard querying logic, causal ordering around the DLQ, and schema mappings parsing. +* **Example CLs:** It's a PR and not a CL — Reply to this email directly, view it on GitHub <#3899?email_source=notifications&email_token=ABSOX5SJGQSPXKIWLAVUXL3466W5LA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINBVGU4TGNJZGEY2M4TFMFZW63VKON2WE43DOJUWEZLEUVSXMZLOOSWGM33PORSXEX3DNRUWG2Y#pullrequestreview-4455935911>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABSOX5VL55U6LRG4NPFBMA3466W5LAVCNFSM6AAAAAC2AKSSEOVHI2DSMVQWIX3LMV43YUDVNRWFEZLROVSXG5CSMV3GSZLXHM2DINJVHEZTKOJRGE> . Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/notifications/mobile/ios/ABSOX5UN4MPPSWBZGMYUYGL466W5LA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINBVGU4TGNJZGEY2M4TFMFZW63VKON2WE43DOJUWEZLEUVSXMZLOOSVGM33PORSXEX3JN5ZQ> and Android <https://github.com/notifications/mobile/android/ABSOX5RRMMCUQJQAPCTDQB3466W5LA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINBVGU4TGNJZGEY2M4TFMFZW63VKON2WE43DOJUWEZLEUVSXMZLOOSXGM33PORSXEX3BNZSHE33JMQ>. Download it today! You are receiving this because you are subscribed to this thread.Message ID: <GoogleCloudPlatform/DataflowTemplates/pull/3899/review/4455935911@ github.com>

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.30%. Comparing base (b8ef535) to head (93a5ed2).
⚠️ Report is 24 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3899      +/-   ##
============================================
+ Coverage     55.55%   63.30%   +7.75%     
+ Complexity     7022     2317    -4705     
============================================
  Files          1103      514     -589     
  Lines         67557    29969   -37588     
  Branches       7576     3303    -4273     
============================================
- Hits          37529    18972   -18557     
+ Misses        27612    10031   -17581     
+ Partials       2416      966    -1450     

Components	Coverage Δ
spanner-templates	88.73% <ø> (+0.38%)	⬆️
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	90.16% <ø> (-0.01%)	⬇️
spanner-live-reverse-replication	83.94% <ø> (-0.10%)	⬇️
spanner-bulk-migration	92.58% <ø> (-0.01%)	⬇️
gcs-spanner-dv	90.39% <ø> (+1.44%)	⬆️
see 621 files with indirect coverage changes

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