docs(examples): honest unversioned fallback for the lineage tutorial's AGENT_VERSION

Greptile P1: a fixed 0.1.0 default would stamp every unlabeled build with
a real-looking version, misattributing traces across commits. The fallback
is now the explicit sentinel 'unversioned'.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: max-parke-scale

examples/tutorials/00_sync/080_lineage/Dockerfile

@@ -47,8 +47,9 @@ ENV PYTHONPATH=/app
 ENV AGENT_NAME=s080-lineage
 
 # The agent build version stamped onto every span as __agent_version__.
-# Real deployments pass the image tag or git SHA at build time.
-ARG AGENT_VERSION=0.1.0
+# Pass the image tag or git SHA at build time; the fallback is an explicit
+# sentinel so an unlabeled build never fabricates a version.
+ARG AGENT_VERSION=unversioned
 ENV AGENT_VERSION=${AGENT_VERSION}
 
 # Run the agent using uvicorn

examples/tutorials/00_sync/080_lineage/README.md

@@ -32,8 +32,9 @@ lineage service; edges are derived later from materialized traces
 
 - **`__agent_version__`** — the SGP tracing processor stamps the
   `AGENT_VERSION` env var onto every span. The Dockerfile sets it from a
-  build arg; real deployments pass the image tag or git SHA. For
-  `agentex agents run`, export it or put it in this directory's `.env`.
+  build arg (pass the image tag or git SHA; unlabeled builds fall back to
+  the explicit sentinel `unversioned` rather than a fabricated version).
+  For `agentex agents run`, export it or put it in this directory's `.env`.
 
 Ref namespaces must use the canonical URI forms from the lineage identifier
 conventions (`packages/sgp-lineage/docs/event-contract.md` in `scaleapi`);