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."""

tests/test_metadata_internals.py

@@ -13,6 +13,7 @@ from PIL import Image
 from remove_ai_watermarks._internal.c2pa import (
     _parse_c2pa_chunk,
     c2pa_info_from_manifest_store,
+    c2pa_info_has_removal_hint,
     cbor_text_after,
     extract_c2pa_chunk,
     extract_c2pa_info,
@@ -209,6 +210,64 @@ class TestC2PA:
         assert info["ai_tool"] == "Dreamina"
         assert info["c2pa_identity_ai"] is True
 
+    def test_structured_invismark_exposes_algorithm_and_watermark_id(self):
+        watermark_id = "83424621-03cb-40e3-9808-a9fae837156d"
+        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,
+                                    }
+                                ],
+                            },
+                        }
+                    ]
+                }
+            },
+        }
+
+        info = c2pa_info_from_manifest_store(store)
+
+        assert info["soft_binding"] == "Microsoft InvisMark"
+        assert info["soft_binding_algorithm"] == "com.microsoft.invismark.1"
+        assert info["soft_binding_value"] == watermark_id
+
+    def test_soft_binding_value_requires_its_algorithm(self):
+        store = {
+            "active_manifest": "broken",
+            "manifests": {
+                "broken": {
+                    "assertions": [
+                        {
+                            "label": "c2pa.soft-binding",
+                            "data": {"blocks": [{"value": "not-attributable"}]},
+                        }
+                    ]
+                }
+            },
+        }
+
+        assert "soft_binding_value" not in c2pa_info_from_manifest_store(store)
+
+    def test_soft_binding_keeps_invisible_removal_fail_safe(self):
+        assert c2pa_info_has_removal_hint({"soft_binding_vendors": ["Microsoft InvisMark"]}) is True
+
+    def test_content_fingerprint_does_not_trigger_invisible_removal(self):
+        info = {
+            "soft_binding": "Adobe (content fingerprint)",
+            "soft_binding_vendors": ["Adobe (content fingerprint)"],
+        }
+
+        assert c2pa_info_has_removal_hint(info) is False
+
     def test_invalid_ingredient_does_not_taint_active_validation_or_supply_claims(self):
         store = {
             "active_manifest": "update",