Swap: tell the user when a journal is locked out or failing; long names

- SwapManager queues user notices when a journal is held by another kte
  (this session's edits are then not journaled) and, once per gap, when
  journal writes fail. Editor shows them in the status line from its
  per-frame hook. Both went only to the error log, so crash recovery was
  silently off or incomplete.
- The fallback swap name '<basename>.<hash>.swp' exceeded NAME_MAX for
  basenames over ~233 bytes, so such files were never journaled; the
  basename is shortened (on a UTF-8 boundary) only in that case.
- Audit doc: sixth-round findings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015rcVQiiWyTzoNrsvLSaAfB

docs/audits/claude-findings-20260923.md

@@ -444,6 +444,23 @@ before the fix (unless noted).
   passed under a correctly instrumented ASan build with leak checks,
   and the stress fuzzers ran with ASan and UBSan.)
 
+**Sixth round (real terminal, file I/O, recovery end to end)**
+- UTF-8 typed or pasted over a slow link lost characters: with the
+  input batch read at zero timeout, ncurses gave up on a character split
+  across reads and discarded the rest as invalid. kte now assembles
+  UTF-8 itself and waits for continuation bytes. (This regression came
+  from this audit's own input batching.)
+- Visual-line (multi-line) insert, delete, backspace and newline used
+  the cursor's byte column on every selected line, splitting multibyte
+  characters on the others; the column is now carried in characters.
+- Journal failures reached only the error log: a session locked out of
+  the journal by another kte (which only happens when the other opened
+  the file before this one's first edit), or whose journal writes
+  failed, silently had no or partial crash recovery. The status line now
+  says so (once per failure).
+- Basenames over about 233 bytes produced a swap name over NAME_MAX, so
+  such files were never journaled.
+
 **Known limitations (not fixed)**
 - Catastrophic regex backtracking (e.g. `(a*)*b`) can still take very
   long; std::regex has no time limit.
@@ -452,6 +469,9 @@ before the fix (unless noted).
 - GUI-only items B7, B8, B10 and highlighter edge cases B13 are
   unchanged; the ImGui and Qt frontends could not be built in the review
   environment (changed GUI files were syntax-checked where possible).
+- Journals are created at the first edit, so a second kte that opens
+  the file before the first one edits it is not warned at open; the
+  session that is locked out is told at its first edit instead.
 - A journal whose buffer exceeds 16 MiB cannot be checkpointed; after a
   lost record such a journal stays incomplete until the file is saved
   (reported to the user).