Read the InvisMark soft-binding algorithm and its signed watermark id

Reachable c2pa.soft-binding assertions now surface their exact alg and the
bounded printable block value next to the normalized vendor label; a value
without its algorithm stays hidden because it cannot be attributed.
com.microsoft.invismark.1 uses that value as the pixel-watermark identifier
in Microsoft Paint output, so identify names it, metadata carries it, and an
InvisMark soft binding keeps the invisible-removal gate fail-safe even after
C2PA asset binding goes invalid. Content fingerprints still do not trigger
pixel regeneration. Removal is verified against Microsoft's Content
Provenance Detection API, which reports Watermark and C2PA separately; the
protocol and the pixel-identical control requirement are documented.

Implemented in a parallel session; verified, gated, and committed by pi.

pre-commit: 1) maintain.sh - exit 1 on the known uv-secure lightning PYSEC-2026-3624 triage (no fix available, unchanged from 0.29.0); ruff, pyright src/, and 1391 tests passed separately; 2) /simplify - single-pass, clean; 3) docs sync - five docs updated by the author session, no remaining references found; 4) CLAUDE.md - invariants recorded in module-internals, no change needed

tests/test_identify.py

@@ -1144,6 +1144,36 @@ class TestIdentifySoftBinding:
         assert any("Digimarc" in w for w in r.watermarks)
         assert any(s.name == "soft_binding" for s in r.signals)
 
+    def test_invismark_signal_lists_signed_watermark_id(self, tmp_path: Path):
+        watermark_id = "83424621-03cb-40e3-9808-a9fae837156d"
+        record = {
+            "c2pa_store": {
+                "active_manifest": "paint",
+                "manifests": {
+                    "paint": {
+                        "assertions": [
+                            {
+                                "label": "c2pa.soft-binding",
+                                "data": {
+                                    "alg": "com.microsoft.invismark.1",
+                                    "blocks": [{"scope": "the entire image", "value": watermark_id}],
+                                },
+                            }
+                        ]
+                    }
+                },
+            }
+        }
+        evidence = evidence_from_metadata_record(record, path=tmp_path / "paint.png")
+
+        report = identify_from_evidence(evidence)
+
+        assert evidence.ai_metadata["soft_binding_value"] == watermark_id
+        signal = next(signal for signal in report.signals if signal.name == "soft_binding")
+        assert "com.microsoft.invismark.1" in signal.detail
+        assert watermark_id in signal.detail
+        assert any("may remain in the pixels" in caveat for caveat in report.caveats)
+
 
 class TestIdentifyIptcAi:
     """IPTC 2025.1 AISystemUsed drives an AI verdict + platform attribution."""