diff --git a/tests/playwright/rendering-invariants.spec.ts b/tests/playwright/rendering-invariants.spec.ts
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+import { test, expect } from "@playwright/test";
+import { waitForHtmx } from "./helpers";
+
+/**
+ * Rendering-invariant audit coverage.
+ *
+ * Each test in this file pins a dashboard rendering assumption that was
+ * previously NOT exercised by any Playwright test (audit performed against
+ * route inventory in serve/mod.rs vs goto/request URLs in tests/playwright).
+ *
+ * Categories of assumption:
+ *   1. Routes never navigated end-to-end (just smoke-tested for status):
+ *      /eu-ai-act, /matrix/cell, /help/docs/{slug},
+ *      /artifacts/{id}/preview, /artifacts/{id}/graph, /embed/...
+ *   2. Render-shape contracts that aren't pinned:
+ *      mermaid in artifact `description` field; ego-graph svg-viewer
+ *      wrapping; embed-layout vs page-layout structural difference.
+ *   3. Variant-scoping limitations: graph_view doesn't accept variant —
+ *      this is currently silent. Pin it so a future intent change is gated.
+ *   4. Status-code conventions for missing items: artifact_detail returns
+ *      200 (not 404) for unknown IDs; same for results detail.
+ *
+ * If any of these tests starts failing, that's not necessarily a bug — it
+ * may be an intentional architectural change. But it should be a CONSCIOUS
+ * change, not a silent regression.
+ */
+
+test.describe("Rendering invariants — uncovered routes", () => {
+  test("/eu-ai-act renders a real dashboard page (not just 200)", async ({
+    page,
+  }) => {
+    // Route is currently never navigated by any Playwright test. The handler
+    // takes no params and may render either the schema-loaded dashboard or
+    // a "schema not loaded" stub. Both are valid; assert one of them rendered.
+    const resp = await page.goto("/eu-ai-act");
+    expect(resp?.status()).toBe(200);
+    await expect(page.locator("h2")).toContainText("EU AI Act Compliance");
+    // Layout must wrap the content — direct browser GETs go through
+    // the wrap_full_page middleware.
+    await expect(page.locator("nav[role='navigation']")).toBeVisible();
+  });
+
+  test("/help/docs/{slug} renders a topic with a back-link to /help/docs", async ({
+    page,
+  }) => {
+    // The slug index (/help/docs) is tested but no test ever opens an actual
+    // topic page. `cli` is one of the built-in slugs in rivet-cli/src/docs.rs.
+    const resp = await page.goto("/help/docs/cli");
+    expect(resp?.status()).toBe(200);
+    // Topic page must offer a way back to the topic list.
+    await expect(page.locator('a[href="/help/docs"]')).toBeVisible();
+    // Topic body is wrapped in a .card.
+    await expect(page.locator(".card")).toBeVisible();
+    // Layout middleware wraps the partial — nav should be present.
+    await expect(page.locator("nav[role='navigation']")).toBeVisible();
+  });
+
+  test("/artifacts/{id}/preview returns a hover-tooltip fragment", async ({
+    page,
+  }) => {
+    // The preview endpoint is hit by hx-get hover handlers in artifact lists,
+    // but no Playwright test navigates it directly. Pin its fragment shape:
+    // it must render INSIDE the layout when accessed directly (because the
+    // wrap_full_page middleware wraps non-HTMX GETs), and the inner fragment
+    // must use the .art-preview class hierarchy.
+    const resp = await page.goto("/artifacts/REQ-001/preview");
+    expect(resp?.status()).toBe(200);
+    // The art-preview wrapper is the contract used by the hover-tooltip CSS.
+    const preview = page.locator(".art-preview").first();
+    await expect(preview).toBeVisible();
+    // The header carries a type badge + the artifact ID.
+    await expect(preview.locator(".art-preview-header")).toContainText(
+      "REQ-001",
+    );
+    // Title must be present (REQ-001's title in dogfood data is non-empty).
+    await expect(preview.locator(".art-preview-title")).toBeVisible();
+  });
+
+  test("/artifacts/{id}/graph renders an ego-graph wrapped in svg-viewer", async ({
+    page,
+  }) => {
+    // Pins that the per-artifact ego-graph view follows the same
+    // .svg-viewer + toolbar invariant as /graph and /doc-linkage.
+    // No existing test exercises this route end-to-end (the
+    // diagram-viewer.spec.ts list omits it).
+    const resp = await page.goto("/artifacts/REQ-001/graph");
+    expect(resp?.status()).toBe(200);
+    await waitForHtmx(page);
+
+    const viewer = page.locator("#ego-graph-viewer");
+    await expect(viewer).toBeVisible({ timeout: 10_000 });
+    await expect(viewer).toHaveClass(/svg-viewer/);
+
+    // Same three controls as the main /graph view.
+    const toolbar = viewer.locator(".svg-viewer-toolbar");
+    await expect(toolbar.locator("button[title='Zoom to fit']")).toBeVisible();
+    await expect(toolbar.locator("button[title='Fullscreen']")).toBeVisible();
+    await expect(
+      toolbar.locator("button[title='Open in new window']"),
+    ).toBeVisible();
+
+    // Hops control round-trips the request.
+    await expect(page.locator("#hops")).toBeVisible();
+  });
+
+  test("/matrix/cell returns a link list fragment", async ({ page }) => {
+    // The matrix cell drill-down (HTMX-loaded into the matrix table) has
+    // never been navigated end-to-end. We force a direct browser GET; the
+    // wrap_full_page middleware will wrap the partial in the layout, so we
+    // assert on the inner <ul> shape that the matrix view's HTMX target
+    // expects.
+    const resp = await page.goto(
+      "/matrix/cell?source_type=requirement&target_type=feature&link_type=verifies&direction=backward",
+    );
+    expect(resp?.status()).toBe(200);
+    // The fragment is always a <ul> — empty when no links match (renders
+    // a single .meta li), populated otherwise. Pin the wrapper. The list
+    // is rendered as the FIRST direct child of main#content (the layout
+    // middleware wraps the bare fragment).
+    const fragment = page.locator("main#content > ul");
+    await expect(fragment).toBeVisible();
+    // Should not contain server errors.
+    const html = await page.content();
+    expect(html).not.toContain("thread 'main' panicked");
+    expect(html).not.toContain("500 Internal Server Error");
+  });
+});
+
+test.describe("Rendering invariants — embed layout", () => {
+  test("/embed/artifacts/REQ-001 uses embed_layout (no nav, no shell)", async ({
+    page,
+  }) => {
+    // /embed/* is the prefix used by the oembed endpoint to produce an
+    // iframe-friendly view (referenced in api.spec.ts for oembed but never
+    // navigated). Pin the structural difference between embed_layout and
+    // page_layout: embed has no navigation sidebar.
+    const resp = await page.goto("/embed/artifacts/REQ-001");
+    expect(resp?.status()).toBe(200);
+    // No top-level nav element.
+    await expect(page.locator("nav[role='navigation']")).toHaveCount(0);
+    // No .shell wrapper either (that's the page_layout signature).
+    await expect(page.locator("body > .shell")).toHaveCount(0);
+    // But the artifact content IS rendered into <main id="content">.
+    await expect(page.locator("main#content")).toBeVisible();
+    await expect(page.locator("main#content")).toContainText("REQ-001");
+  });
+});
+
+test.describe("Rendering invariants — render-shape contracts", () => {
+  test("mermaid in artifact `description` renders as <pre class='mermaid'>", async ({
+    page,
+  }) => {
+    // ARCH-CORE-001 has a fenced ```mermaid block in its `description` (see
+    // artifacts/architecture.yaml). The markdown renderer in
+    // rivet-core/src/markdown.rs converts these to <pre class="mermaid">
+    // so the dashboard's mermaid.js loader picks them up.
+    //
+    // We pin TWO things at once:
+    //   1. The fenced block IS recognised and emitted as <pre.mermaid>.
+    //   2. Description-mermaid is currently NOT wrapped in .svg-viewer
+    //      (only the dedicated `diagram:` field is). This asymmetry is a
+    //      known UX gap; if it changes, this assertion forces the change
+    //      to be intentional.
+    await page.goto("/artifacts/ARCH-CORE-001");
+    await waitForHtmx(page);
+
+    // The description is in a <dd class="artifact-desc">.
+    const desc = page.locator("dd.artifact-desc");
+    await expect(desc).toBeVisible();
+
+    // Inside that description, mermaid block was emitted as <pre.mermaid>.
+    const mermaidPre = desc.locator("pre.mermaid");
+    await expect(mermaidPre).toBeVisible();
+    // Body should contain the diagram source so mermaid.js can render it.
+    await expect(mermaidPre).toContainText("flowchart");
+
+    // Pinning the current asymmetry: the description-embedded mermaid is
+    // NOT inside an .svg-viewer wrapper. (Only the top-level `diagram:`
+    // field gets one — see render/artifacts.rs:489.)
+    const wrappedInViewer = await desc
+      .locator(".svg-viewer pre.mermaid")
+      .count();
+    expect(wrappedInViewer).toBe(0);
+  });
+});
+
+test.describe("Rendering invariants — variant scoping coverage", () => {
+  test("/graph?variant=minimal-ci is silently UNSCOPED (graph_view ignores variant)", async ({
+    page,
+  }) => {
+    // graph_view in rivet-cli/src/serve/views.rs uses GraphParams (not
+    // ViewParams) and has no `variant` field. The query param is silently
+    // dropped. This means /graph?variant=... renders the FULL graph, not
+    // a variant-scoped subgraph.
+    //
+    // This is currently architecturally intentional (graph layout is
+    // expensive enough that variant scoping was deferred) but it's surprising
+    // for users coming from /artifacts?variant=... which IS scoped. Pin the
+    // current behavior so a future variant-scoping addition is gated.
+    const resp = await page.goto("/graph?variant=minimal-ci&types=requirement");
+    expect(resp?.status()).toBe(200);
+    // Page renders normally.
+    await expect(page.locator("h2")).toContainText("Traceability Graph", {
+      timeout: 30_000,
+    });
+    // The variant banner from layout reflects the URL's variant param.
+    // (The layout ALWAYS shows the banner when ?variant= is present, even
+    // when the handler ignores it — this is the surprising part to pin.)
+    await expect(page.locator(".variant-banner")).toBeVisible();
+  });
+});
+
+test.describe("Rendering invariants — not-found status conventions", () => {
+  test("/artifacts/UNKNOWN-ID returns 200 with 'Not Found' body (not 404)", async ({
+    page,
+  }) => {
+    // artifact_detail in rivet-cli/src/serve/views.rs always returns
+    // Html(...).into_response() — i.e. status 200 — even when the artifact
+    // doesn't exist. The render layer just emits "<h2>Not Found</h2>".
+    //
+    // This is consistent with /externals/<unknown-prefix> (already pinned at
+    // externals.spec.ts:80) but inconsistent with the gut expectation of
+    // 404. Pin the current behavior so any future move to proper 404 is a
+    // conscious decision.
+    const resp = await page.goto("/artifacts/DEFINITELY-DOES-NOT-EXIST-ZZZ");
+    expect(resp?.status()).toBe(200);
+    await expect(page.locator("body")).toContainText("Not Found");
+    // The layout still wraps it (nav present).
+    await expect(page.locator("nav[role='navigation']")).toBeVisible();
+  });
+});
+
+test.describe("Rendering invariants — search fragment shape", () => {
+  test("/search with empty query returns the cmd-k empty-state fragment", async ({
+    page,
+  }) => {
+    // The search handler returns a FRAGMENT (no <html> shell when accessed
+    // via HTMX) but routes.spec.ts only smoke-tests with ?q=OSLC. The
+    // empty-query branch (line 56-60 of render/search.rs) emits a specific
+    // .cmd-k-empty placeholder. Pin its shape so the cmd-k UI keeps working.
+    //
+    // Direct browser GET goes through wrap_full_page so we get the layout
+    // wrapping; the fragment lives inside main#content.
+    const resp = await page.goto("/search");
+    expect(resp?.status()).toBe(200);
+    const empty = page.locator(".cmd-k-empty").first();
+    await expect(empty).toBeVisible();
+    await expect(empty).toContainText(/Type to search/i);
+  });
+
+  test("/search?q=zzznonexistentzzz emits empty-results fragment", async ({
+    page,
+  }) => {
+    // Pins the no-results branch (line 189-194 of render/search.rs).
+    const resp = await page.goto("/search?q=zzznonexistentzzz");
+    expect(resp?.status()).toBe(200);
+    const empty = page.locator(".cmd-k-empty").first();
+    await expect(empty).toBeVisible();
+    await expect(empty).toContainText(/No results/i);
+  });
+});