diff --git a/src/portfolio_optimiser/provenance.py b/src/portfolio_optimiser/provenance.py
new file mode 100644
index 0000000..d2210f1
--- /dev/null
+++ b/src/portfolio_optimiser/provenance.py
@@ -0,0 +1,57 @@
+"""First-class Pydantic provenance stamp.
+
+Provenance is authoritative framework data — **independent** of MAF's ``Annotation`` type,
+which silently drops on the Python streaming path (#4316, research 02 Dim 2). A
+``ProvenanceStamp`` is a Pydantic model that must carry at least one ``Citation`` (a
+``min_length=1`` constraint), the model + role that produced the proposal, the validator's
+decision, and the token usage. ``to_annotations()`` maps to MAF ``Annotation`` dicts for
+DISPLAY only — never the source of truth.
+
+The locator type (``TextSpan``) is owned by ``retrieval.py`` (Step 5) and imported here, so
+a citation's span is the same exact object the retriever produced.
+"""
+
+from __future__ import annotations
+
+from typing import Literal
+
+from agent_framework import Annotation, TextSpanRegion
+from pydantic import BaseModel, Field
+
+from portfolio_optimiser.retrieval import TextSpan
+
+
+class Citation(BaseModel):
+    """One exact-span citation into a source document (locator owned by retrieval.py)."""
+
+    file: str
+    locator: TextSpan
+    snippet: str
+
+
+class ProvenanceStamp(BaseModel):
+    """Authoritative provenance for one proposal — at least one citation is mandatory."""
+
+    citations: list[Citation] = Field(min_length=1)
+    model: str
+    role: str
+    validator_decision: Literal["validated", "rejected"]
+    token_usage: int
+
+    def to_annotations(self) -> list[Annotation]:
+        """Map to MAF ``Annotation`` dicts for display only (NOT the source of truth)."""
+        return [
+            Annotation(
+                type="citation",
+                snippet=c.snippet,
+                annotated_regions=[
+                    TextSpanRegion(
+                        type="text_span",
+                        start_index=c.locator.start_index,
+                        end_index=c.locator.end_index,
+                    )
+                ],
+                additional_properties={"file": c.file},
+            )
+            for c in self.citations
+        ]
diff --git a/tests/test_provenance.py b/tests/test_provenance.py
new file mode 100644
index 0000000..08a4d71
--- /dev/null
+++ b/tests/test_provenance.py
@@ -0,0 +1,47 @@
+"""Step 6 tests — first-class Pydantic provenance stamp.
+
+At least one citation is mandatory (the load-bearing NFR); a valid stamp exposes the
+proposal's provenance fields; the annotation adapter yields MAF citation dicts for display.
+Pattern: tests/spikes/test_c_validator.py (pydantic raises + field assertions).
+"""
+
+import pytest
+from pydantic import ValidationError
+
+from portfolio_optimiser.provenance import Citation, ProvenanceStamp
+from portfolio_optimiser.retrieval import TextSpan
+
+
+def _stamp() -> ProvenanceStamp:
+    return ProvenanceStamp(
+        citations=[Citation(file="asphalt.txt", locator=TextSpan(0, 10), snippet="0123456789")],
+        model="qwen3:4b",
+        role="proposer",
+        validator_decision="validated",
+        token_usage=42,
+    )
+
+
+def test_zero_citations_is_rejected() -> None:
+    with pytest.raises(ValidationError):
+        ProvenanceStamp(
+            citations=[],
+            model="m",
+            role="proposer",
+            validator_decision="validated",
+            token_usage=1,
+        )
+
+
+def test_valid_stamp_exposes_provenance_fields() -> None:
+    stamp = _stamp()
+    assert len(stamp.citations) >= 1
+    assert stamp.model and stamp.role
+    assert stamp.validator_decision in {"validated", "rejected"}
+    assert isinstance(stamp.token_usage, int) and stamp.token_usage > 0
+
+
+def test_to_annotations_yields_citation_dicts() -> None:
+    anns = _stamp().to_annotations()
+    assert anns and all(a["type"] == "citation" for a in anns)
+    assert anns[0]["annotated_regions"][0]["type"] == "text_span"