fix: preserve persistence health across page splits

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Summary

• preserve historical unsized-page identities across same-batch splits and removals
• convert the missing table-of-contents page panic into an actionable persistence error
• catch persistence worker panics and expose terminal health immediately
• prepare WorkTable 1.0.0-beta.9

Incident reproduced

AgencyZero 3.20 hit page should be available in table of contents while repeatedly upserting variable-sized settings values. The KV persistence worker died, but the process continued accepting writes until quit attempted a drain roughly twenty minutes later.

The added repeated_string_upsert regression uses the same key/value shape, 256 keys, and 1,000 varying-size upserts. It deterministically reproduced the original panic before the fix and now passes.

A separate lifecycle test deliberately panics a persistence worker and verifies that wait_for_failure reports the terminal error immediately.

Root cause

A split can change a physical page maximum, then a later removal in the same persistence batch can lower it again. A subsequent insert may still reference the pre-split/pre-removal maximum. The table-of-contents lookup had already discarded that historical identity, so the worker panicked. The fix keeps batch-scoped aliases and resolves updates through the current buffered page key.

Verification

• cargo test: 174 library tests, 522 integration tests passed; 4 ignored
• doctests: 2 passed
• cargo clippy --all-targets -- -D warnings
• deterministic 1,000-upsert regression passes
• persistence panic lifecycle test passes

Review focus

Please scrutinize alias lifetime and collision behavior, same-batch split/remove/insert ordering, terminal lifecycle transitions, panic payload conversion, and whether any generated table API can miss a worker failure.