[ISSUE #10878] fix(tieredstore): read across all file segments

[yuluo-yx]

Which Issue(s) This PR Fixes

• Fixes [Bug] FlatAppendFile readAsync truncates reads spanning more than two segments #10878

Brief Description

FlatAppendFile.readAsync now collects reads from every intersecting committed segment and combines them in order. The previous one- or two-segment fast behavior remains, while a three-segment regression now returns all 250 requested bytes.

How Did You Test This Change?

• mise exec java@zulu-8.94.0.17 -- mvn -pl tieredstore -am -DskipITs -Dtest=FlatAppendFileTest -Dsurefire.failIfNoSpecifiedTests=false test (7 tests passed)
• Checkstyle and SpotBugs passed in the same Maven reactor.
• git diff --check and the 400-line scope gate passed.
• Not run: full repository build, container tests, or end-to-end tests.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 48.30%. Comparing base (fd0c959) to head (8f59244).

Files with missing lines	Patch %	Lines
...ache/rocketmq/tieredstore/file/FlatAppendFile.java	94.73%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10888      +/-   ##
=============================================
- Coverage      48.39%   48.30%   -0.09%     
+ Complexity     13562    13535      -27     
=============================================
  Files           1380     1380              
  Lines         101165   101172       +7     
  Branches       13127    13126       -1     
=============================================
- Hits           48962    48876      -86     
- Misses         46233    46308      +75     
- Partials        5970     5988      +18     

☔ 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.

[RockteMQ-AI]

Summary

Review of PR #10888: [ISSUE #10878] fix(tieredstore): read across all file segments

This PR modifies 2 file(s) with 45 additions and 14 deletions.
Changes look reasonable. No critical issues found in the diff.

---

Automated review by github-manager-bot

[RockteMQ-AI]

Summary

This PR generalizes FlatAppendFile.readAsync() to read across an arbitrary number of file segments instead of the previous hard-coded 2-segment limit. The implementation uses a loop to iterate segments and CompletableFuture.allOf() for parallel reads, then combines results into a single ByteBuffer.

The fix is correct: the loop properly tracks readOffset and remainingLength, and the segment length calculation handles boundary conditions. The test covers the 3-segment case. LGTM.

---

Automated review by github-manager-bot