fix: partial write support and default write endpoint

[alespour]

Proposed Changes

This PR finalizes partial-write support and fixes regression issue with the default API endpoint behavior introduced in PR #365.

• The client defaults to the V2 API endpoint for writes for broad product compatibility. Since the Java client has not been released yet with the PR feat: support partial writes #365 behavior, this change is not breaking.
• V3 API-only options:
  • noSync
  • acceptPartial

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• Tests pass
• Commit messages are conventional

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.29%. Comparing base (23b16a4) to head (f4c6464).

Files with missing lines	Patch %	Lines
...nfluxdb/v3/client/internal/InfluxDBClientImpl.java	77.77%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #388      +/-   ##
==========================================
+ Coverage   88.25%   88.29%   +0.04%     
==========================================
  Files          21       21              
  Lines        1532     1546      +14     
  Branches      277      279       +2     
==========================================
+ Hits         1352     1365      +13     
- Misses         82       83       +1     
  Partials       98       98              

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[Copilot]

Pull request overview

This PR restores V2 write endpoint defaults while preserving V3-only partial-write and noSync support behind useV2Api=false.

Changes:

• Defaults write routing to the V2 API endpoint and updates related tests/expectations.
• Refines V2/V3 method-not-allowed error messages and partial-write error formatting.
• Updates README and changelog language around partial writes and endpoint compatibility.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/main/java/com/influxdb/v3/client/write/WriteOptions.java	Changes default write endpoint selection to V2 and updates validation/docs.
src/main/java/com/influxdb/v3/client/internal/InfluxDBClientImpl.java	Adds endpoint-specific 405 guidance for V2 and V3 writes.
src/main/java/com/influxdb/v3/client/internal/RestClient.java	Adjusts partial-write detail rendering and fallback JSON token formatting.
src/main/java/com/influxdb/v3/client/InfluxDBClient.java	Updates public configuration documentation.
src/main/java/com/influxdb/v3/client/config/ClientConfig.java	Updates write endpoint configuration documentation.
src/test/java/...	Updates and expands tests for defaults, routing, validation, and error formatting.
README.md	Documents default V2 writes and V3-only write options.
CHANGELOG.md	Records partial-write support and V2 default behavior.

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[karel-rehor]

ad hoc implementation works for use cases mentioned in README.md regarding new write arguments nosync, useV2Api (true and false) and acceptPartial. Checked both ClientConfig settings and WriteOptions settings passed in client.writeRecords(). Calls used partial values generated in line protocol batches.

Tests run using OpenJdk 24.0.2. are passing.

Looks good to me. 🚴 🏁

Just need to rebase with the main branch.