fix(newos4): empty-pipeline crash, stacks in reports, frame in digest + dashboard (v4.6.55)

Root cause: splitPipe() splits on every '|', so `help |`, `| wc -l`, `a || b` produced a stage with
no argv and executePipeChain() called parts[0].toLowerCase() on undefined — 989 occurrences, first
filed 2026-10-20, unfixable from the report because bug reports dropped the stack that named
executePipeChain:3955. Same unguarded read existed in _classify().

- terminal.js: _classify() returns an inert classification for empty argv; executePipeChain()
  parses each stage once, filters stages with no argv (so the last real stage stays final), warns
  only when the whole pipeline is empty. Last-stage test now compares against the filtered length.
- module-system.js: `bug` diagnostics include the stack (10 frames, 1200 chars); auto-filed reports
  carry it too — they are the majority of the inbox and were previously message-only.
- report.php: per-stack 2 KB cap; fingerprint pinned to message/source/count so adding `stack`
  cannot break dedupe against reports filed before today.
- ingest.php: first_frame() parsed once on ingest, stored as `frame` on each signature.
- newos4-triage.py: FRAME| line with the first application frame.
- dashboard.php: frame under each Top Errors row.
- modules/test/test-pipe-guard.js: ordering tripwire (guard must precede the parts[0] read).

Verified: test RED exit=1 -> GREEN exit=0; browser matrix on v4.6.55 (help |, | wc -l,
echo hi || echo bye, ls | | wc -l, |) -> 0 new error signatures, "|" warns;
auto-filed report now carries stack (RPT-...f3e31124, archived after the probe);
frame = modules/core/core-bundle.js:3955:42; maintain OK; skill audit 7/7.

1 files changed, 4 insertions, 0 deletions

diff --git a/modules/core/module-system.js b/modules/core/module-system.js
index bedceef..e7f7e5a 100644
--- a/modules/core/module-system.js
+++ b/modules/core/module-system.js
@@ -334,6 +334,10 @@
                             message: String(e.message || e.msg || '').slice(0, 300),
                             source: String(e.source || e.url || '').slice(0, 200),
                             count: Number(e.count) || 1,
+                            // The stack is the only thing that makes a report actionable; it was
+                            // dropped here while ingest kept it, which is why the 2026-10-20
+                            // `toLowerCase` report could not be localised for three days.
+                            stack: e.stack ? String(e.stack).split('\n').slice(0, 10).join('\n').slice(0, 1200) : null,
                         }));
                     } catch (_e) {}
                     try {