feat(ts): opt-in import_style=modules and oneof_style=discriminated for TS generators

[hishamank]

Summary

Adds two orthogonal, opt-in plugin options to both TypeScript generators (protoc-gen-ts-client, protoc-gen-ts-server), parsed from the protoc parameter string:

• import_style=modules — emit one canonical type module per proto file (<proto>.ts) with cross-file imports, plus a single shared errors.ts, instead of inlining the full type closure into every service file. Service files become slimmed clients/servers that import their request/response types. Fixes the type-duplication problem (e.g. SongID/ValidationError re-declared in every service file).
• oneof_style=discriminated — render un-annotated (non-synthetic) oneofs as $case discriminated unions instead of flattened optional fields. An explicit sebuf.http oneof_config annotation still wins.

Defaults are import_style=inline / oneof_style=flatten.

Backward compatibility

With no options, output is byte-for-byte identical to today. This is enforced by the design: the existing emitter functions become thin wrappers that delegate to new *Ctx variants with a nil context; a nil/inline context resolves every type reference to its bare name and records no import. All existing goldens are unchanged (the new behavior lives in new golden subdirectories).

⚠️ import_style=modules requires strategy: all

The modules layout emits shared files (errors.ts, cross-package type modules). buf's default strategy: directory invokes the plugin once per directory, which would emit those shared files repeatedly. Set strategy: all on the plugin in buf.gen.yaml when using import_style=modules:

plugins:
  - local: protoc-gen-ts-client
    out: ./web
    strategy: all
    opt:
      - import_style=modules
      - oneof_style=discriminated

Implementation

• internal/tscommon/config.go — Options + ParseOptions (ignores unknown keys like paths=source_relative; errors on bad values).
• internal/tscommon/imports.go — EmitContext + ImportTracker (relative specifier computation, deterministic collision aliasing, type-only vs value imports).
• internal/tscommon/modules.go — EmitSharedModules: per-proto type modules grouped by source file + shared errors.ts; reserved-name guard (ValidationError/ApiError/FieldViolation).
• internal/tscommon/types.go — *Ctx variants of the emitters (nil-wrapper preserves defaults); SynthesizeOneofInfo ($case); MessagesBySourceFile/EnumsBySourceFile.
• Generators branch to modules mode and thread an EmitContext through type/enum reference sites; the shared type modules emitted by client and server are byte-identical.

Tests / verification

• go vet ./... + full suite green (9 packages). Existing inline goldens unchanged.
• New golden cases (separate subdirs) for both generators: import_style=modules (per-proto module + slimmed service file + shared errors.ts) and oneof_style=discriminated ($case unions). Client/server shared type modules verified byte-identical.
• Unit tests: ParseOptions, RelativeImportSpecifier, ImportTracker (collision aliasing, render ordering).
• End-to-end against a real multi-package schema (anghamna, with strategy: all): 98 files, 0 duplicate-file warnings, SongID defined once and imported, oneofs discriminated, and the full tree type-checks under tsc --strict --moduleResolution bundler.

Follow-ups (out of scope)

• A dedicated multi-package golden fixture (cross-package imports are covered by the e2e run for now).
• Docs page for the TS generator options.

[github-actions]

🔍 CI Pipeline Status

❌ Lint: failure
✅ Test: success
✅ Coverage: success
⚠️ Build: skipped
⚠️ Integration: skipped

---

📊 Coverage Report: Available in checks above
🔗 Artifacts: Test results and coverage reports uploaded

[codecov]

Codecov Report

❌ Patch coverage is 26.50273% with 269 lines in your changes missing coverage. Please review.
✅ Project coverage is 4.09%. Comparing base (ad6a1b5) to head (30482a9).

Files with missing lines	Patch %	Lines
internal/tscommon/modules.go	0.00%	82 Missing ⚠️
internal/tscommon/types.go	0.00%	66 Missing ⚠️
internal/tscommon/imports.go	66.34%	33 Missing and 2 partials ⚠️
internal/tsservergen/modules.go	0.00%	29 Missing ⚠️
internal/tsclientgen/modules.go	0.00%	26 Missing ⚠️
internal/tsservergen/generator.go	0.00%	18 Missing ⚠️
internal/tsclientgen/generator.go	0.00%	11 Missing ⚠️
internal/tscommon/config.go	93.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #198      +/-   ##
========================================
+ Coverage   3.32%   4.09%   +0.76%     
========================================
  Files         62      67       +5     
  Lines      10966   11290     +324     
========================================
+ Hits         365     462      +97     
- Misses     10595   10819     +224     
- Partials       6       9       +3     

Flag	Coverage Δ
unittests	4.09% <26.50%> (+0.76%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[hishamank]

Split into two independently-reviewable PRs so each feature can be accepted on its own:

• feat(ts): emit discriminated-union oneofs in TS generators #199 — oneof_style=discriminated (smaller, self-contained)
• feat(ts): emit per-proto type modules + shared errors in TS generators #200 — import_style=modules (stacked on feat(ts): emit discriminated-union oneofs in TS generators #199)

Closing this combined PR in favor of those.