Select task FU-P13-T11: Preserve JSON-RPC numeric request ID fidelity in broker transport

[SoundBlaster]

Description

Replace lossy 20-bit integer ID masking in broker/transport.py with a reversible per-session counter mapping so all valid JSON-RPC request IDs (large, negative, concurrent) round-trip exactly to clients.

Root cause: _process_client_line applied original_id & 0xFFFFF to integer IDs before encoding them into the composite broker_id. This silently truncated IDs > 1,048,575, mangled negative IDs, and could alias two distinct IDs that shared the same lower 20 bits.

Fix: A shared monotonic counter (_alloc_local_id) assigns a unique local alias to every incoming ID (integer or string). A reverse map (id_restore) enables O(1) restoration on the response path, replacing the previous O(n) linear scan of string_id_map.

Changes:

• broker/types.py — added int_id_map, id_restore, _next_local_id fields to ClientSession
• broker/transport.py — added _alloc_local_id() helper; updated _process_client_line, route_upstream_response, _drain_session; updated module docstring
• tests/unit/test_broker_transport.py — fixed 3 existing tests; added 5 new TestIntegerIDFidelity tests

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Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring
• CI/CD improvement

This is a bug fix — integer ID fidelity was silently broken for IDs outside the 20-bit range.

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Quality Gates

Check	Result
make test	526 passed, 9 skipped (≥90% coverage)
make lint	ruff check src/ — all checks passed
make format	No format issues
make typecheck	mypy src/mcpbridge_wrapper/broker/ — success, no issues in 5 source files
make doccheck	N/A (no docs/ changes)

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Documentation Sync

• Documentation changes are synced with DocC catalog — N/A (no docs/ files modified)

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Testing

• Added/updated tests for new functionality
  • TestIntegerIDFidelity::test_large_integer_id_round_trips (ID = 2²¹)
  • TestIntegerIDFidelity::test_negative_integer_id_round_trips (ID = -1)
  • TestIntegerIDFidelity::test_concurrent_int_ids_no_collision (IDs 1 and 1+2²⁰)
  • TestIntegerIDFidelity::test_integer_id_reuses_existing_mapping
  • TestIntegerIDFidelity::test_int_and_string_id_no_collision
• All tests pass locally
• Manually tested the changes — N/A (broker requires macOS + Xcode)

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Checklist

• Code follows the project's style guidelines
• Self-review completed
• Comments added for complex code (updated module docstring in transport.py)
• Documentation updated (if needed) — N/A
• No new warnings generated
• PR title is descriptive