Descriptor-phase errnos in readTextForDiff fold to before: null so a file
deleted or made unreadable after the caller's preflight cannot fail the
committed write; cancellation and non-errno faults still propagate. Drops
the now-covered isFile v8 ignore, extends llm-replay with catalog
capability parity (defaultMaxTokens/reasoningEfforts), and records the
fs-write-overwrite-bounded keyless snapshot pinning the over-limit
whole-file fallback through the real acp-agent composition.
Rebuild of the fs-overwrite-diff-bound branch on current master. Adds the
diffBasisMaxBytes Config field (10 MiB default, capped by runtime
allocation/decode limits), gates both overwrite sides, and reads the prior
basis from the bounded opened descriptor in cancellation-aware chunks; any
post-stat size change returns a null basis. Also pins the one-extra-byte
growth probe with a regression and drops the now-covered v8 ignore.
ZiyaZhang