docs(ingest): note suppressed metric is external-path-only (review round 3)

The inline _process_pdf path does not emit document_escalation_suppressed_total;
the "what-if OCR" counter is instrumented only on the per-tier external path
(evaluate_escalation / _parse_pdf_tier). Comment the inline OCR gate so a reader
doesn't mistake the omission for a bug. Deferred the assert_never nit (typing
.assert_never is 3.11+; Literal+frozen already guard construction) and the
pre-existing minimum-ValueError pass (only "ocr"/None are ever passed).

Deck #324.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/document_processors/registry.py

@@ -247,6 +247,13 @@ class ProcessorRegistry:
             result, content, settings, record=True, filename=filename
         )
 
+        # NOTE: the suppressed-escalation metric (document_escalation_suppressed_total,
+        # the "what-if OCR" signal; Deck #324) is intentionally NOT emitted on this
+        # inline/memory path -- it is instrumented only on the per-tier external
+        # path (vector/processor._parse_pdf_tier via evaluate_escalation). When OCR
+        # is off here the would-be escalation is simply not taken (the gate below);
+        # operators reading the suppressed counter are on the procrastinate fleet.
+        #
         # Escalate scanned / no-text-layer PDFs to OCR (tier-3) when enabled and
         # a provider is registered. The fast tier is terminal otherwise. Note: a
         # fast FAILURE (encrypted/corrupt -- result.success False, no