fix(shard): widen partition repair when a view-adopted suffix is missing bodies

[mattp5657]

Closes

#4075

Rationale

A partition group can wedge permanently and stop committing after a view change lands while a node is mid-restart, hanging every producer to that partition until its read timeout expires.

What changed?

After a view change, a backup that adopts a StartView suffix advances its sequencer to the new head immediately, but repair only fetched bodies up to the commit point when the replica also had a commit lag, which a just-restarted node always does. The adopted op's body was never fetched. Once any later op advanced the sequencer past it, the backup's replication gap check rejected every retransmission of the missing op as a stale duplicate, permanently, and commit could never advance past it.

Widens the repair fetch window using missing_suffix, already computed for this but not consulted in this branch, so the first repair pass covers the adopted suffix before anything else can move the sequencer past it.

Fixes cluster::fast_primary_rejoin::given_a_quic_producer_when_its_first_roster_hop_is_down_should_reach_the_partition_primary, failing ~70-90% of local runs and on all 4 CI attempts.

Local Execution

• Passed. Fixed test: 12/12 runs. WebSocket sibling: 5/5. Full fast_primary_rejoin.rs (8 tests), full cluster:: integration suite (61 tests), and consensus/partitions/shard unit suites (462 tests): all pass, no regressions.
• Pre-commit hooks: not run through this session; cargo fmt, cargo sort --no-format, and cargo clippy were run manually.

AI Usage

Claude was used in the generation of this.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 44.84%. Comparing base (7b78014) to head (3408b8f).

Files with missing lines	Patch %	Lines
core/shard/src/lib.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #4074       +/-   ##
=============================================
- Coverage     85.55%   44.84%   -40.71%     
  Complexity     1402     1402               
=============================================
  Files          1241     1240        -1     
  Lines        186306   155199    -31107     
  Branches     152594   121489    -31105     
=============================================
- Hits         159395    69605    -89790     
- Misses        22865    83746    +60881     
+ Partials       4046     1848     -2198     

Components	Coverage Δ
Rust Core	35.32% <66.66%> (-51.14%)	⬇️
Java SDK	67.29% <ø> (ø)
C# SDK	56.94% <ø> (-20.09%)	⬇️
Python SDK	90.06% <ø> (ø)
PHP SDK	85.65% <ø> (ø)
Node SDK	94.50% <ø> (-1.74%)	⬇️
Go SDK	69.35% <ø> (+0.03%)	⬆️

Files with missing lines	Coverage Δ
core/shard/src/lib.rs	69.46% <66.66%> (-12.25%)	⬇️

... and 653 files with indirect coverage changes

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[ethanlin01x]

LGTM

[ethanlin01x]

nit: Could you add a unit test for the commit_lag && missing_suffix case?