[glue] Make On-Demand Reshare Artifacts Finalization-Safe

[patrick-ogrady]

Stacked on #4364.

Summary

• Keep speculative epoch artifact requests lazy and FIFO, materializing one ancestry view at a time in a cancellable actor-selected scan.
• Prioritize admitted finalized-block reports over speculative scan completion, re-anchor interrupted scans after durable progress, and return Pending when terminal finalization cannot safely classify an unmaterialized request.
• Bind verification and artifact reuse to the exact dealer-log view, preserving completed speculative verdicts while deriving the canonical artifact at the epoch boundary.
• Keep the mailbox transport-only and accept proposal- and verification-shaped ancestry without requiring an immediately available head.
• Add deterministic coverage for stalled, truncated, and detached ancestry; cancellation; FIFO ordering; exact-view caching; and finalization races.

LOC (classification boundary: the top-level #[cfg(test)] in each file): production +209/-220; tests and test infrastructure +665/-178.

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[github-actions]

Benchmark results

Regressions: 0.

✅ `qmdb::merkleize/v=any::unordered::fixed::mmr k=10000 ch=false s=true cc=true` (2/2 gates passed)

Field	Value
Package	commonware-storage
Benchmark target	qmdb_gungraun
Variant	qmdb::merkleize/v=any::unordered::fixed::mmr k=10000 ch=false s=true cc=true
Filter	*::bench_merkleize::any_unordered_fixed_mmr
Baseline suite	commonware-storage
Gates	EstimatedCycles should decrease; tolerance 10.00%; blob_reads should decrease; tolerance 10.00%
Cargo flags	--features test-traits

Metric	Baseline	Current	Delta	Gate
Ir	13,627,399	13,123,083	-3.70%	-
L1hits	17,436,376	16,763,229	-3.86%	-
LLhits	142,432	93,579	-34.30%	-
RamHits	20,720	13,110	-36.73%	-
TotalRW	17,599,528	16,869,918	-4.15%	-
EstimatedCycles	18,873,736	17,689,974	-6.27%	EstimatedCycles should decrease; tolerance 10.00%
blob_reads	158	158	+0.00%	blob_reads should decrease; tolerance 10.00%

✅ `qmdb::merkleize/v=current::ordered::fixed::mmb chunk=256 k=10000 ch=false s=true cc=true` (2/2 gates passed)

Field	Value
Package	commonware-storage
Benchmark target	qmdb_gungraun
Variant	qmdb::merkleize/v=current::ordered::fixed::mmb chunk=256 k=10000 ch=false s=true cc=true
Filter	*::bench_merkleize::current_ordered_fixed_mmb_chunk_256
Baseline suite	commonware-storage
Gates	EstimatedCycles should decrease; tolerance 10.00%; blob_reads should decrease; tolerance 10.00%
Cargo flags	--features test-traits

Metric	Baseline	Current	Delta	Gate
Ir	15,479,128	15,529,065	+0.32%	-
L1hits	20,275,864	20,413,526	+0.68%	-
LLhits	137,999	138,409	+0.30%	-
RamHits	17,336	17,895	+3.22%	-
TotalRW	20,431,199	20,569,830	+0.68%	-
EstimatedCycles	21,572,619	21,731,896	+0.74%	EstimatedCycles should decrease; tolerance 10.00%
blob_reads	235	235	+0.00%	blob_reads should decrease; tolerance 10.00%

Baseline commit(s): dfe4c5a9ab89

[codecov]

Codecov Report

❌ Patch coverage is 96.39344% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.51%. Comparing base (59f615d) to head (2e12e8e).
⚠️ Report is 1 commits behind head on cl/precompute-artifacts.

Files with missing lines	Patch %	Lines
glue/src/dkg/reshare/actor/inclusion.rs	97.14%	10 Missing and 5 partials ⚠️
glue/src/dkg/reshare/mailbox.rs	89.70%	5 Missing and 2 partials ⚠️

@@                     Coverage Diff                     @@
##           cl/precompute-artifacts    #4520      +/-   ##
===========================================================
- Coverage                    95.51%   95.51%   -0.01%     
===========================================================
  Files                          606      605       -1     
  Lines                       273973   273860     -113     
  Branches                      6601     6585      -16     
===========================================================
- Hits                        261697   261580     -117     
- Misses                       10086    10098      +12     
+ Partials                      2190     2182       -8     

Files with missing lines	Coverage Δ
glue/src/dkg/reshare/application.rs	95.00% <100.00%> (+0.16%)	⬆️
glue/src/dkg/reshare/mailbox.rs	83.23% <89.70%> (+4.18%)	⬆️
glue/src/dkg/reshare/actor/inclusion.rs	96.08% <97.14%> (+1.66%)	⬆️

... and 39 files with indirect coverage changes

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