fix(stream): bound range reads by metadata entries

[wengsht]

Problem

Stream metadata defines the logical first and last live entry IDs, but the shared range path scans the raw RocksDB entry-key interval supplied by the caller.

If raw keys outside the metadata bounds remain after an interrupted or older slot migration, they become visible again through XRANGE, XREVRANGE, and new-message XREADGROUP reads. This makes XLEN / XINFO STREAM disagree with XRANGE and can pin retention: a sweeper repeatedly starts from a stale pre-frontier entry while XTRIM correctly treats the newer metadata frontier as authoritative.

The completed #3592 prevents new trim DeleteRange records from being lost during incremental slot migration, but existing divergent streams still need a read-side invariant.

Change

Clamp the shared stream range interval to metadata's [first_entry_id, last_entry_id] bounds:

• forward and reverse reads use the same logical bounds;
• exclusion flags are cleared only when their boundary was replaced by a metadata bound;
• metadata-empty streams return no entries even if stale raw keys exist.

This is read-only hardening. It does not add cleanup writes to read commands or change stream metadata.

Test

The regression trims a stream, reinserts raw entry keys below and above its metadata bounds, and verifies:

• forward range returns only metadata-live entries;
• reverse range returns only metadata-live entries;
• an exact lookup of a stale entry returns empty.

Validation:

• ./x.py format
• ./x.py check format
• fresh ./x.py build build-make --unittest -j 8
• all 99 RedisStreamTest.* cases pass

AI assistance was used for diagnosis and drafting; I reviewed the code and tests.

[Copilot]

Pull request overview

Bounds stream range reads to metadata-defined live entries, preventing stale RocksDB keys from resurfacing.

Changes:

• Clamp forward and reverse ranges to metadata bounds.
• Preserve endpoint exclusion semantics.
• Add regression coverage for stale raw entries.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/types/redis_stream.cc	Enforces metadata bounds in shared range reads.
tests/cppunit/types/stream_test.cc	Tests forward, reverse, and exact stale-entry reads.

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