diff --git a/backend/src/workspaces/contracts.ts b/backend/src/workspaces/contracts.ts
index 8b25998c..eec16656 100644
--- a/backend/src/workspaces/contracts.ts
+++ b/backend/src/workspaces/contracts.ts
@@ -230,14 +230,20 @@ function evidenceDocumentation(
     ];
   }
   const evidenceVariables = variables.filter(({ role }) => role === "EVIDENCE");
+  const requiredVariables = evidenceVariables.filter(({ suffix }) => suffix !== "SESSION_TOKEN_FILE");
+  const optionalVariables = evidenceVariables.filter(({ suffix }) => suffix === "SESSION_TOKEN_FILE");
   return [
     ...common,
     ...details,
     `- Maximum chunk characters: \`${policy.max_chunk_chars}\``,
     `- Retained published generations: \`${policy.retain_published_generations}\``,
-    ...(evidenceVariables.length === 0 ? [] : [
+    ...(requiredVariables.length === 0 ? [] : [
       "- Required installation file variables:",
-      ...evidenceVariables.map(({ name }) => `  - \`${name}\``),
+      ...requiredVariables.map(({ name }) => `  - \`${name}\``),
+    ]),
+    ...(optionalVariables.length === 0 ? [] : [
+      "- Optional installation file variables:",
+      ...optionalVariables.map(({ name }) => `  - \`${name}\``),
     ]),
     "",
   ];
diff --git a/backend/test/routes-workspaces.test.ts b/backend/test/routes-workspaces.test.ts
index 41938a9b..f5849d45 100644
--- a/backend/test/routes-workspaces.test.ts
+++ b/backend/test/routes-workspaces.test.ts
@@ -615,6 +615,24 @@ test("real publish create/update, pull, list, and read preserve a complete Evide
       baseCommit: createdRevision.commit, baseBlob: createdRevision.blob,
     },
   });
+  expect(update.statusCode).toBe(200);
+  await realGit(fixture.author, ["pull", "--ff-only", "origin", "main"]);
+  const remotelyEdited = validateCanonicalWorkspace({
+    ...updated,
+    evidence: {
+      ...updated.evidence,
+      policy: { max_chunk_chars: 9_001, retain_published_generations: 9 },
+    },
+  });
+  writeFileSync(
+    join(fixture.author, "workspaces", "research-clinical.yaml"),
+    serializeWorkspaceYaml(remotelyEdited),
+  );
+  await realGit(fixture.author, ["add", "workspaces/research-clinical.yaml"]);
+  await realGit(fixture.author, ["commit", "-m", "Remote Evidence-only descriptor edit"]);
+  await realGit(fixture.author, ["push", "origin", "main"]);
+  const remoteCommit = await realGit(fixture.author, ["rev-parse", "HEAD"]);
+
   const pull = await fixture.app.inject({ method: "POST", url: "/workspace-registry/pull" });
   const list = await fixture.app.inject({ method: "GET", url: "/workspaces" });
   const read = await fixture.app.inject({ method: "GET", url: "/workspaces/research-clinical" });
@@ -623,10 +641,12 @@ test("real publish create/update, pull, list, and read preserve a complete Evide
   expect(create.statusCode).toBe(200);
   expect(update.statusCode).toBe(200);
   expect(pull.statusCode).toBe(200);
+  expect(pull.json().head).toBe(remoteCommit);
   expect(list.statusCode).toBe(200);
-  expect(list.json().find(({ id }: { id: string }) => id === "research-clinical").workspace).toEqual(updated);
+  expect(list.json().find(({ id }: { id: string }) => id === "research-clinical").workspace)
+    .toEqual(remotelyEdited);
   expect(read.statusCode).toBe(200);
-  expect(read.json().workspace).toEqual(updated);
+  expect(read.json().workspace).toEqual(remotelyEdited);
 });
 
 test("real route reports a safe field for an Evidence-only concurrent edit", async () => {
@@ -697,11 +717,18 @@ test.each([
     label: "inline S3 credential field",
     source: { type: "s3", uri: "s3://clinical-evidence/published/", access_key: SECRET_CANARY },
   },
-])("real validate rejects $label without echoing it", async ({ source }) => {
+])("real publish rejects $label without echoing it or changing HEAD", async ({ source }) => {
   const fixture = await createRealRouteFixture();
+  await fixture.registry.bootstrap();
+  const base = await fixture.registry.read("psd-clinical");
+  const invalid = structuredClone(base.workspace) as any;
+  invalid.evidence = { source };
   const response = await fixture.app.inject({
-    method: "POST", url: "/workspaces/validate",
-    payload: { workspace: { ...workspace, evidence: { source } } },
+    method: "POST", url: "/workspaces/publish",
+    payload: {
+      action: "update", workspace: invalid,
+      baseCommit: base.revision.commit, baseBlob: base.revision.blob,
+    },
   });
 
   expect(response.statusCode).toBe(400);
diff --git a/backend/test/workspace-registry.test.ts b/backend/test/workspace-registry.test.ts
index f0f24136..6eb096b2 100644
--- a/backend/test/workspace-registry.test.ts
+++ b/backend/test/workspace-registry.test.ts
@@ -1013,13 +1013,17 @@ test("snapshots canonical Evidence artifacts at the active commit without copyin
   const committedDescriptor = parseWorkspaceYaml(await gitOutput(remote.source, [
     "show", `${remote.initialCommit}:workspaces/psd-clinical.yaml`,
   ])) as CanonicalWorkspace;
+  const committedBlob = await gitOutput(remote.source, [
+    "rev-parse", `${remote.initialCommit}:workspaces/psd-clinical.yaml`,
+  ]);
+  expect(active.revision.blob).toBe(committedBlob);
   expect(expectedFiles["psd-clinical.yaml"]).toBe(serializeWorkspaceYaml(committedDescriptor));
   expect(readdirSync(snapshotDirectory).sort()).toEqual([
     "psd-clinical.env.example", "psd-clinical.md", "psd-clinical.yaml", "snapshot.json",
   ]);
   expect(manifest.head).toBe(remote.initialCommit);
   expect(manifest.revisions[0]).toMatchObject({
-    id: "psd-clinical", commit: remote.initialCommit, blob: active.revision.blob,
+    id: "psd-clinical", commit: remote.initialCommit, blob: committedBlob,
   });
   expect(Object.keys(manifest.files).sort()).toEqual(Object.keys(expectedFiles).sort());
   for (const [name, contents] of Object.entries(expectedFiles)) {
diff --git a/backend/test/workspaces-contracts.test.ts b/backend/test/workspaces-contracts.test.ts
index 2ac47f83..7cb11a07 100644
--- a/backend/test/workspaces-contracts.test.ts
+++ b/backend/test/workspaces-contracts.test.ts
@@ -444,6 +444,25 @@ test.each(evidenceSources)("renders deterministic public Evidence docs for $labe
   }
 });
 
+test("documents the S3 session token file as optional", () => {
+  const descriptor = parseWorkspaceYaml(
+    `${renderWorkspaceWithoutEvidence()}evidence:
+  source: { type: s3, uri: s3://clinical-evidence/published/, credentials: static_files }
+`,
+  );
+  const markdown = renderWorkspaceDocs(descriptor).markdown;
+  const required = markdown.slice(
+    markdown.indexOf("- Required installation file variables:"),
+    markdown.indexOf("- Optional installation file variables:"),
+  );
+  const optional = markdown.slice(markdown.indexOf("- Optional installation file variables:"));
+
+  expect(required).toContain("EVIDENCE_ACCESS_KEY_FILE");
+  expect(required).toContain("EVIDENCE_SECRET_KEY_FILE");
+  expect(required).not.toContain("EVIDENCE_SESSION_TOKEN_FILE");
+  expect(optional).toContain("EVIDENCE_SESSION_TOKEN_FILE");
+});
+
 test("documents same-revision filesystem ownership without claiming P1 materialization", () => {
   const descriptor = parseWorkspaceYaml(
     `${renderWorkspaceWithoutEvidence()}evidence:\n  source: { type: filesystem, uri: workspace-content/psd-clinical/evidence }\n`,