feat(identify): detect Dreamina C2PA + Tencent Cloud AIGC schema

Two AI-provenance metadata types mined from the retained corpus that
identify previously read as no-signal:

- Dreamina (ByteDance's international Jimeng brand) signs C2PA as
  "Bytedance Pte. Ltd." with a "Dreamina/x.y" claim generator and NO
  digitalSourceType, so the generator name is the only AI signal. Add a
  C2paAiVendor row with a new asserts_ai flag (identity-AI: presence
  asserts AI without trainedAlgorithmicMedia) plus the derived
  C2PA_IDENTITY_AI_ORGS view, folded into identify's c2pa_is_ai. Keyed on
  the Dreamina generator token, not the "Bytedance Pte" issuer, so non-AI
  CapCut edits signed by the same entity stay unattributed. 7/7 corpus
  files now attribute to ByteDance.

- Tencent Cloud's TC260 AIGC variant uses a ServiceProvider/ServiceUser
  schema (vs the producer-side ContentProducer schema), embedded in EXIF
  ImageDescription; add those field names to _TC260_FIELDS so the generic
  {"AIGC":{...}} gate accepts it. 11/11 corpus files now flagged.

Test-first: reproducing tests in test_identify.py / test_metadata.py.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/remove_ai_watermarks/identify.py

@@ -41,7 +41,12 @@ from remove_ai_watermarks.metadata import (
     xai_signature,
 )
 from remove_ai_watermarks.noai.c2pa import cbor_text_after, extract_c2pa_info, soft_binding_vendors_in
-from remove_ai_watermarks.noai.constants import C2PA_AI_TOOLS, C2PA_AI_VENDORS, C2PA_ISSUERS
+from remove_ai_watermarks.noai.constants import (
+    C2PA_AI_TOOLS,
+    C2PA_AI_VENDORS,
+    C2PA_IDENTITY_AI_ORGS,
+    C2PA_ISSUERS,
+)
 from remove_ai_watermarks.watermark_registry import GEMINI_SPARKLE_TRUST_CONF
 
 if TYPE_CHECKING:
@@ -515,7 +520,14 @@ def identify(image_path: Path, *, check_visible: bool = True, check_invisible: b
             c2pa_source_kind = "generated"
         elif b"compositeWithTrainedAlgorithmicMedia" in head:
             c2pa_source_kind = "enhanced"
-    c2pa_is_ai = c2pa_source_kind is not None
+    # An identity-AI issuer (a pure-generator brand like Dreamina) asserts AI even
+    # without a digitalSourceType -- some ByteDance/Dreamina manifests ship no
+    # trainedAlgorithmicMedia, so the registered generator name is the only signal.
+    # Restricted to the ``asserts_ai`` vendors (distinctive brand strings), so it
+    # does not reopen the incidental-mention problem the common-word issuers have.
+    issuer_blob = " ".join(issuers)
+    c2pa_identity_ai = has_c2pa and any(org in issuer_blob for org in C2PA_IDENTITY_AI_ORGS)
+    c2pa_is_ai = c2pa_source_kind is not None or c2pa_identity_ai
     # Generator string (for the signal detail): structured for PNG, CBOR-scanned
     # for other containers. Best-effort -- some manifests key it as
     # `claim_generator_info` (Pixel), so this can be None even when a device is

src/remove_ai_watermarks/metadata.py

@@ -137,6 +137,7 @@ AIGC_MARKERS: tuple[bytes, ...] = (
 # label even when the namespaced XMP element is absent.
 _TC260_FIELDS: frozenset[str] = frozenset(
     {
+        # Producer-side schema (Doubao and most China-served generators).
         "Label",
         "ContentProducer",
         "ProduceID",
@@ -144,6 +145,12 @@ _TC260_FIELDS: frozenset[str] = frozenset(
         "PropagateID",
         "ReservedCode1",
         "ReservedCode2",
+        # Service-provider schema (Tencent Cloud's AIGC variant, mined from the
+        # retained corpus 2026-07): the same ``{"AIGC":{...}}`` wrapper but keyed
+        # ``ServiceProvider`` / ``ServiceUser`` (+ generic ``Time`` / ``ContentId``,
+        # not gated on), embedded in EXIF ``ImageDescription``.
+        "ServiceProvider",
+        "ServiceUser",
     }
 )
 

src/remove_ai_watermarks/noai/constants.py

@@ -100,6 +100,13 @@ class C2paAiVendor(NamedTuple):
     # (usually a shorter form of org, e.g. "Google" for "Google LLC"); None when platform is.
     needle: str | None
     synthid: bool = False  # vendor pairs an invisible SynthID pixel watermark with its C2PA manifest
+    # The vendor's mere presence in the manifest asserts AI generation even without
+    # a digitalSourceType (``trainedAlgorithmicMedia``) assertion. Set ONLY for a
+    # pure-generator brand whose issuer/generator byte string is unambiguous (e.g.
+    # "Dreamina"). Do NOT set for common-word issuers (Adobe/Google/OpenAI/Microsoft):
+    # those appear incidentally in unrelated XMP/trust-chain bytes, so they stay
+    # source-type-gated in identify._attribute_platform.
+    asserts_ai: bool = False
 
 
 # C2PA known vendors, ORDERED for first-match-wins platform attribution: when a
@@ -149,6 +156,24 @@ C2PA_AI_VENDORS: tuple[C2paAiVendor, ...] = (
     # earlier row's label wins anyway -- they normalize together for clash
     # detection. Verified on real signed files in production traffic, 2026-06-19.
     C2paAiVendor(b"Byteplus", "BytePlus (ByteDance)", "ByteDance (Doubao / Jimeng / Volcano Engine)", "ByteDance"),
+    # Dreamina (ByteDance's international Jimeng brand) signs C2PA as "Bytedance
+    # Pte. Ltd." with a "Dreamina/x.y" claim generator and, unlike the Volcano
+    # Engine output, NO digitalSourceType assertion -- so the generator name is the
+    # only AI signal. It is registered by that generator token (which the caBX /
+    # store-JSON byte scan sees across active + ingredient manifests, where the
+    # active manifest is often a plain c2pa-tool transcode). ``asserts_ai`` lets the
+    # issuer alone flag AI without trainedAlgorithmicMedia; "Dreamina" is a
+    # distinctive brand string, so it does not risk the incidental-mention problem
+    # the common-word issuers have. Verified on real signed files in the retained
+    # corpus, 2026-07. Normalizes to the same "ByteDance" needle/platform as the
+    # volcengine row (they collapse together for clash detection).
+    C2paAiVendor(
+        b"Dreamina",
+        "ByteDance (Dreamina)",
+        "ByteDance (Doubao / Jimeng / Volcano Engine)",
+        "ByteDance",
+        asserts_ai=True,
+    ),
     # Canva Magic Media signs AI-generated images as "Canva" with a generic
     # c2pa-rs claim generator + trainedAlgorithmicMedia; without this entry the
     # source read AI but no platform was attributed. Verified on real signed files
@@ -181,6 +206,12 @@ C2PA_AI_VENDORS: tuple[C2paAiVendor, ...] = (
 # C2PA issuer signature -> resolved org name, for the manifest byte-scan.
 C2PA_ISSUERS: dict[bytes, str] = {v.issuer: v.org for v in C2PA_AI_VENDORS}
 
+# Resolved org names of the vendors whose presence asserts AI generation on its
+# own (no digitalSourceType needed) -- see the ``asserts_ai`` field. identify uses
+# this to lift the AI verdict for an identity-AI issuer (e.g. Dreamina) that ships
+# no trainedAlgorithmicMedia. Derived from the flag -- set it on the vendor, not here.
+C2PA_IDENTITY_AI_ORGS: frozenset[str] = frozenset(v.org for v in C2PA_AI_VENDORS if v.asserts_ai)
+
 # C2PA issuers whose signed outputs also carry an invisible SynthID pixel
 # watermark -- a metadata proxy for "SynthID is in the pixels":
 #   - Google (Imagen/Gemini): embeds SynthID, long-standing (DeepMind docs).