diff --git a/src/portfolio_optimiser/run.py b/src/portfolio_optimiser/run.py
index 2bdfc48..b8ea642 100644
--- a/src/portfolio_optimiser/run.py
+++ b/src/portfolio_optimiser/run.py
@@ -190,11 +190,19 @@ async def run_project(
     gen_context = debate_output or context
 
     # 5. Structured candidate -> blocking validation; token bound = the meter in this loop.
-    outcome = await generate_via_llm(factory("proposer"), project, gen_context, meter)
+    proposer_client = factory("proposer")
+    outcome = await generate_via_llm(proposer_client, project, gen_context, meter)
     proposal = outcome.proposal
 
     # 6. First-class provenance stamp (authoritative; independent of MAF Annotation).
-    model = "fake-model" if client_factory is not None else resolve_model(profile, "proposer")
+    # F1: an injected client_factory stamps the injected client's REAL model ("unknown" is the
+    # neutral fallback for a client that doesn't surface one -- never a fabricated name); the
+    # default path keeps the deterministic resolve_model.
+    model = (
+        (getattr(proposer_client, "model", None) or "unknown")
+        if client_factory is not None
+        else resolve_model(profile, "proposer")
+    )
     stamp = ProvenanceStamp(
         citations=citations,
         model=model,
diff --git a/tests/test_vertical_slice_e2e.py b/tests/test_vertical_slice_e2e.py
index 63006f2..34bd6c3 100644
--- a/tests/test_vertical_slice_e2e.py
+++ b/tests/test_vertical_slice_e2e.py
@@ -41,6 +41,24 @@ async def test_a_valid_proposal_end_to_end(docs_dir, make_client_factory, fresh_
     assert stamp.token_usage > 0  # sourced from the synthetic UsageDetails
 
 
+async def test_a1_provenance_stamps_injected_client_model_not_sentinel(
+    docs_dir, make_client_factory, fresh_store
+) -> None:
+    """F1 regression: an injected client_factory must stamp the injected client's REAL model
+    (SyntheticUsageChatClient.model == 'synthetic'), never the 'fake-model' literal — the leak
+    falsified provenance on the public deployer seam (run.py:197)."""
+    result = await run_project(
+        "FV42-GSV-E1",
+        "local",
+        docs_dir=docs_dir,
+        verdict_input=_VI,
+        client_factory=make_client_factory(_VALID),
+        store=fresh_store,
+    )
+    assert result.provenance.model == "synthetic"
+    assert result.provenance.model != "fake-model"
+
+
 async def test_b_out_of_range_is_rejected(docs_dir, make_client_factory, fresh_store) -> None:
     result = await run_project(
         "FV42-GSV-E1",