feat(gossip): priority channels, noise tolerance, amplification, random walk - #2250

- Make DEFAULT_GOSSIP_CONFIG neutral/empty; add EXAMPLE_GOSSIP_CONFIG for tests.
- Add config parameter to GossipProtocol and gossip() for explicit setup.
- Report attempted/successful/failed targets and only mark a node propagated when at least one write succeeds.
- Add mempalace_gossip to service.WRITE_TOOLS and invariant test.

Refs MemPalace#2239

Add a rooms field to ChatterNode and match hallway co-occurrence rooms against
node rooms rather than hall names. Regression test uses a room (audit_report)
that differs from the node hall (security) to prove the namespaces are no
longer conflated.

Refs MemPalace#2247

…mPalace#2221)

The MemPalace#2221 fix reached develop through MemPalace#2228 at an earlier revision of the
branch, so three guards and their tests did not come with it. One of the
three is a regression the gate that did land introduced.

sweep_directory: the new gate probes the file type with f.stat() inside a
try, and its except OSError printed SKIP and continued. A dangling symlink,
a symlink loop and a file unlinked between rglob and the gate all raise
there. Before the gate existed each of them reached sweep(), raised, and was
appended to failures — so the gate turned "could not read this transcript"
into a silent skip and a successful exit. A probe that FAILS is an error,
not a benign file type: log it, print WARNING, book it in failures. A probe
that succeeds and reports a non-regular file still skips silently.

_parse_gradle: the is_file() gate sat in front of the try whose except
OSError the parser already had, so a manifest under a directory with r but
no x raised PermissionError out of a call that used to answer "no manifest
name". The gate moves inside that try. _collect_manifest_names stats with
os.path.isfile, which reports instead of raising, matching the parsers it
guards.

split_file: the type gate in main() covers the files the glob listed, but
split_file builds its output names itself, so a pre-existing FIFO at one of
them wedged write_text in the kernel waiting for a reader. Output names that
are anything but a regular file are skipped.

That gate asks os.path.lexists, not os.path.exists. exists() follows the
link, so a DANGLING symlink at an output name reads as "nothing there" and
the write goes through it, creating the target — a chunk landing wherever
the link points rather than in the output directory. Measured: the two calls
differ on that one case and agree on every other (regular file, symlink to a
file, missing name, FIFO, symlink to FIFO, directory).

test_gather_origin_samples_survives_an_unreadable_directory broke under root
rather than passing vacuously: CAP_DAC_OVERRIDE walks into the 0o444
directory, the walled-off file stays readable, and the count assertion sees
two samples instead of one. It now carries the same needs_unprivileged_posix
gate as the three new permission tests.

miner._read_text_no_follow: comment fix only. F_SETLEASE on a FIFO fails
EINVAL, not ENXIO — measured on Linux 6.18 / glibc 2.39. The code branches
on EAGAIN and is unaffected.

Per-message try/except so one failing message does not discard unprocessed
siblings or prior children. Requeue children while holding the lock and
reserve capacity against concurrent callers.

Refs MemPalace#2248

- Encode the original predicate in the gossip source_file so viral_facts can
  group by the source fact identity instead of the destination predicate.
- Use one reference timestamp for all as_of metrics (active and expired).
- Format the default reference as canonical UTC to satisfy KG validation.

Refs MemPalace#2249

…om walk