fix(pipeline,api,wing): never archive a note as processed when nothing was ingested; titles do not merge sources; ties prefer the page on disk (review of #211, pass 3)

- in a wing, an ingest that writes no source page is an error: the note goes to
  raw/failed with the warnings in log.md instead of leaving the inbox as
  'processed' (model returned [], only invalid types, only clashing entities)
- the wing's source path is deterministic, so Resolve no longer redirects a
  source onto another note's page because the model gave both the same title
  ('Home'); that overwrote the hash and the text
- a batch tie between concept and entity prefers the page already on disk, so
  its update is not lost; the wing's own source page keeps its slug even when a
  foreign page shares it
- brain_pending lists an unreadable (over-cap) note with the reason instead of
  dropping it; the client filter's 4 KiB match-span limit is documented
Each has a test that fails without it (mutation-checked).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/raw-inbox.md

@@ -12,6 +12,7 @@ with the machines you drop files from. (hyperguild#205, #208, #209)
 | a note whose text matches the client-content pattern, with no folder | parked in `raw/needs-review/`, not extracted |
 | a folder or `wing:` naming an unknown, reserved or non-ASCII wing, or two disagreeing signals | parked in `raw/needs-review/` |
 | a note over the size cap, or one that cannot be archived | stays in `raw/`, reported once, not retried until it changes |
+| a note the model returned nothing usable for (no source page could be written) | fails: the note is kept in `raw/failed/` and the reason is in `log.md`; it is never archived as processed |
 
 Concepts and entities are shared across wings because their slug is the graph's
 identity. A source whose slug is taken gets a wing-qualified one (`notes-homelab`).
@@ -39,6 +40,13 @@ server runs is usable without a restart.
 
 ## Known limits
 
+- The client filter works on 1 MiB chunks that overlap by 4 KiB. A match that can
+  span more than 4 KiB (crafted padding between two words of a multi-word
+  pattern, exactly at a chunk edge) is not guaranteed to be found; this affects
+  notes over 1 MiB only. On a 64 MiB note the check takes about ten seconds.
+- A pattern that matches the empty string (`.*`, `x*`) parks every unsignalled
+  note. That fails closed and only the operator's own configuration can do it.
+
 - A deliberate folder into a sensitive wing places the note there, and the shared
   concept/entity pages then cite that source by title. Client material does not
   belong in the brain at all; the pattern only guards the unsignalled lane.