[release/6.x] Cherry pick: Recovery and Join snapshot ledger offset fix (#7901)

[cjen1-msft]

backport #7901

[achamayou]

@cjen1-msft I think this needs something like #7918 as well as a rev up of the version in pyproject.

[Copilot]

Pull request overview

Backport of #7901 to the 6.x release branch to fix an edge case where recovery/join from a snapshot whose seqno is beyond the end of the available ledger should still resume ledger writing correctly from the snapshot boundary. This is accompanied by new regression coverage in both Python E2E tests and C++ host ledger unit tests.

Changes:

• Update host ledger truncation logic to support a recovery-mode “forward truncate” past current ledger end, and tighten file selection when reading by index.
• Add new recovery/join regression tests which construct ledger variants with snapshot/ledger offsets and verify recovery/join succeeds.
• Bump release version to 6.0.28 and document the fix in the changelog.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/recovery.py	Adds an E2E recovery test that recovers from snapshot/ledger offset variants.
tests/reconfiguration.py	Adds an E2E join-node test that joins from snapshot/ledger offset variants.
tests/infra/utils.py	Adds helper to synthesize ledger chunk files for the new tests.
src/host/test/ledger.cpp	Adds unit tests covering recovery-mode truncation behavior at/beyond ledger end.
src/host/ledger.h	Implements recovery-mode forward truncation and improves file lookup bounds-checking.
python/pyproject.toml	Bumps Python package version to 6.0.28.
CHANGELOG.md	Adds 6.0.28 entry describing the fix.

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