fix(cache): recover unreadable cache rows

[wan9chi]

Motivation

A malformed or incompatible value in the local SQLite cache should not prevent a task from running. Decode failures currently escape cache lookup as fatal errors, and a stale fingerprint can continue pointing at a missing cache entry.

Changes

• Treat unreadable cache values as cache misses so task execution can continue.
• Remove only the exact key and value observed, preserving concurrent replacements.
• Clean up dangling task-fingerprint mappings safely.
• Continue surfacing database access and key-encoding failures as operational errors.
• Report recovered entries in cache status and saved run summaries.

[wan9chi]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• test(cache): cover large and unreadable entries #556
• fix(cache): recover unreadable cache rows #555 👈 (View in Graphite)
• fix(cache): raise cache preallocation limit #554
• main

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