refactor(consensus)!: typed AdvanceOutOfRange variant end-to-end

[SebastianThiebaud]

Summary

Promote the out-of-range high-water advance from a Box<dyn Error>-erased ConsensusError::PermanentDriver source to a first-class ConsensusError::AdvanceOutOfRange(u64) variant. The offending value is carried structurally from the propose-time guard, through the server's disposition layer, into both consumers — no downcasting, no re-boxing in classify.

• Breaking surface (the !): the public AdvanceOutOfRange struct and its pub use re-export are removed from tsoracle-consensus. The only downcaster in the tree was the crate's own test; no external consumer is affected.
• Disposition layer carries the value structurally: PersistDisposition::OutOfRange(u64) instead of Permanent(Box::new(...)). This follows the disposition module's stated design philosophy — "a fifth ConsensusError variant becomes one edit here plus a compiler-forced arm at each site" — and lets the fence path reconstruct ConsensusError::AdvanceOutOfRange(n) faithfully instead of laundering it back into PermanentDriver. service.rs reuses the variant's Display so the message text stays pinned to one source of truth.
• Test strengthening: three driver tests that previously asserted matches!(_, PermanentDriver(_)) on the OOR path now assert the new variant and the carried u64. The unrelated PermanentDriver(_) assertions (storage I/O failpoints, Raft Fatal, paxos PendingReconfig, watch-task death) are untouched.

Blast radius (9 files, +92/−30): the new variant + simplified guard in tsoracle-consensus, the new disposition arm + two compiler-forced consumer arms in tsoracle-server, and three updated test assertions across the file/paxos/openraft drivers.

Test plan

• cargo test --workspace --all-features — 1158 passed, 0 failed, 21 ignored across 135 test result blocks
• cargo clippy --workspace --all-features --all-targets -- -D warnings — clean
• scripts/check-ts-header.py — 270 files OK
• Pre-commit cargo fmt --check + cargo clippy passed
• New unit tests:
  • consensus::advance::tests::reject_out_of_range_advance_rejects_above_the_cap_as_variant
  • consensus::error::tests::consensus_error_display_text (now covers AdvanceOutOfRange)
  • server::persist_disposition::tests::advance_out_of_range_carries_the_offending_value_structurally

[coveralls]

Coverage Report for CI Build 26494250958

Coverage decreased (-0.06%) to 94.848%

Details

• Coverage decreased (-0.06%) from the base build.
• Patch coverage: 13 uncovered changes across 6 files (23 of 36 lines covered, 63.89%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
crates/tsoracle-server/src/service.rs	5	0	0.0%
crates/tsoracle-server/src/fence.rs	4	0	0.0%
crates/tsoracle-consensus/src/advance.rs	4	3	75.0%
crates/tsoracle-driver-openraft/src/driver.rs	2	1	50.0%
crates/tsoracle-driver-paxos/src/driver.rs	2	1	50.0%
crates/tsoracle-server/src/persist_disposition.rs	10	9	90.0%
Total (8 files)	36	23	63.89%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	14966
Covered Lines:	14195
Line Coverage:	94.85%
Coverage Strength:	357048.18 hits per line

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💛 - Coveralls