fix: distinguish install/dual-solve/crystallize failures from success

[dripsmvcp]

five small fixes to code that landed on test, all the same shape — a
failure or not-yet-ready state that was being reported as success. found
while auditing the branch; each has a regression test and none touches the
review gate.

install-mcp (codex toml_merge) — a config.toml the minimal serializer
can't round-trip (a non-bmp string value like an emoji, a nan/inf float)
was bucketed as skipped and printed (already present) with a clean Done,
so the user believes vouch is wired into codex when it isn't. serializer
failure now lands in a distinct failed bucket, is reported as such, and the
command exits non-zero. reproduced end-to-end: an existing config with an
emoji string value → the [mcp_servers.vouch] block silently never installs.

install-mcp path containment — a manifest dst that escapes the target
tree (../absolute) is now refused with an AdapterError instead of writing
outside target. defense in depth for the manifest file writer; every shipped
adapter uses contained relative paths, so no behavior change for real installs.

dual-solve review-ui — _serialize computed the recommendation over the
empty candidate list on every poll, so a running job rendered "neither engine
produced a usable diff" for its entire (multi-minute) duration. the hint is now
omitted until candidates exist.

session.crystallize — retrying on a session that hasn't been ended rewrote
the session-<id> summary page with a fresh wall-clock Ended: stamp each
time (and re-embedded it), so #256's "idempotent retry" wasn't idempotent. an
open session now renders a stable marker; retries produce an identical body.

capture ingest-codex — rollout parsing had no size cap and would read an
oversized (or newline-free-blob) rollout whole into memory. bounded to 64 MiB
up front, matching the byte caps on other untrusted reads.

make check green — pytest (full, excl. embeddings), mypy, ruff.

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