app: persistent agent strip in Diff tab + board-card severity escalation

app/src/components/AgentStrip.test.tsx

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+import { describe, it, expect, vi } from "vitest";
+import { render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { AgentStrip } from "./AgentStrip";
+import { makeFinding } from "../test/fixtures";
+
+describe("AgentStrip — presence", () => {
+  it("renders nothing when there is neither intent nor findings", () => {
+    const { container } = render(
+      <AgentStrip intent={null} findings={[]} onOpenBriefing={vi.fn()} />,
+    );
+    expect(container.firstChild).toBeNull();
+  });
+
+  it("renders with intent only", () => {
+    render(
+      <AgentStrip
+        intent="Streams the parser instead of buffering it."
+        findings={[]}
+        onOpenBriefing={vi.fn()}
+      />,
+    );
+    expect(screen.getByText("AGENT'S READ")).toBeInTheDocument();
+    expect(
+      screen.getByText("Streams the parser instead of buffering it."),
+    ).toBeInTheDocument();
+  });
+
+  it("renders with findings only (no intent)", () => {
+    render(
+      <AgentStrip
+        intent={null}
+        findings={[makeFinding({ id: "a", severity: "Critical" })]}
+        onOpenBriefing={vi.fn()}
+      />,
+    );
+    expect(screen.getByText("AGENT'S READ")).toBeInTheDocument();
+    expect(screen.getByText("CRIT")).toBeInTheDocument();
+  });
+});
+
+describe("AgentStrip — intent line", () => {
+  it("strips markdown to plain text (never renders rich content)", () => {
+    render(
+      <AgentStrip
+        intent="**Bold** intent line"
+        findings={[]}
+        onOpenBriefing={vi.fn()}
+      />,
+    );
+    expect(screen.getByText("Bold intent line")).toBeInTheDocument();
+  });
+});
+
+describe("AgentStrip — severity chips", () => {
+  it("shows a chip per non-zero severity, Info included", () => {
+    render(
+      <AgentStrip
+        intent="does things"
+        findings={[
+          makeFinding({ id: "c1", severity: "Critical" }),
+          makeFinding({ id: "c2", severity: "Critical" }),
+          makeFinding({ id: "w1", severity: "Warning" }),
+          makeFinding({ id: "i1", severity: "Info" }),
+        ]}
+        onOpenBriefing={vi.fn()}
+      />,
+    );
+    expect(screen.getByTitle("2 Critical findings")).toBeInTheDocument();
+    expect(screen.getByTitle("1 Warning finding")).toBeInTheDocument();
+    expect(screen.getByTitle("1 Info finding")).toBeInTheDocument();
+    expect(screen.getByText("CRIT")).toBeInTheDocument();
+    expect(screen.getByText("WARN")).toBeInTheDocument();
+    expect(screen.getByText("INFO")).toBeInTheDocument();
+  });
+
+  it("omits a severity with a zero count", () => {
+    render(
+      <AgentStrip
+        intent="does things"
+        findings={[makeFinding({ id: "w1", severity: "Warning" })]}
+        onOpenBriefing={vi.fn()}
+      />,
+    );
+    expect(screen.getByText("WARN")).toBeInTheDocument();
+    expect(screen.queryByText("CRIT")).not.toBeInTheDocument();
+    expect(screen.queryByText("INFO")).not.toBeInTheDocument();
+  });
+});
+
+describe("AgentStrip — Briefing link", () => {
+  it("invokes onOpenBriefing when the Briefing link is clicked", async () => {
+    const user = userEvent.setup();
+    const onOpenBriefing = vi.fn();
+    render(
+      <AgentStrip
+        intent="does things"
+        findings={[]}
+        onOpenBriefing={onOpenBriefing}
+      />,
+    );
+    await user.click(screen.getByRole("button", { name: /Briefing/ }));
+    expect(onOpenBriefing).toHaveBeenCalledTimes(1);
+  });
+});

app/src/components/AgentStrip.tsx

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+/**
+ * The persistent agent strip for the Diff tab (mockup A2).
+ *
+ * A single always-visible, never-collapsible line directly under the workspace
+ * header carrying the agent's voice: a brand left rail, the `AGENT'S READ`
+ * eyebrow, one plain-text line of the distilled intent (markdown stripped, never
+ * rendered — a clamp of rich text looks broken), the live severity chips for the
+ * review's advisory findings, and a link back to the full Briefing tab.
+ *
+ * Props-driven with no store reads so PR 7's board preview rail can reuse it.
+ * Renders nothing when the review has neither an intent nor any findings, so a
+ * bare review carries no empty strip.
+ */
+
+import type { ReviewFinding } from "../bindings/ReviewFinding";
+import { AgentMark } from "@/lib/agent-event";
+import { findingCounts, severityMeta } from "@/lib/finding-severity";
+import { previewText, stripMarkdown } from "@/lib/markdown-text";
+import { cn } from "@/lib/utils";
+import { ArrowUpRight } from "lucide-react";
+
+interface AgentStripProps {
+  /** The agent's distilled read of what the PR does; null when the pre-pass has not run. */
+  readonly intent: string | null;
+  /** Every advisory finding for the review; drives the live severity chips. */
+  readonly findings: readonly ReviewFinding[];
+  /** Switch the enclosing workspace to the Briefing tab. */
+  readonly onOpenBriefing: () => void;
+}
+
+/**
+ * The Diff tab's agent strip. Intent line + severity chips + a Briefing link, in
+ * the shared agent voice. Renders nothing without an intent or a finding.
+ */
+export function AgentStrip({ intent, findings, onOpenBriefing }: AgentStripProps) {
+  if (intent === null && findings.length === 0) return null;
+
+  const counts = findingCounts(findings);
+  // Every non-zero severity shows on the strip (Info included, unlike the
+  // board cards), highest severity first.
+  const chips = [
+    { count: counts.critical, meta: severityMeta("Critical") },
+    { count: counts.warning, meta: severityMeta("Warning") },
+    { count: counts.info, meta: severityMeta("Info") },
+  ].filter((c) => c.count > 0);
+
+  return (
+    <div className="flex shrink-0 items-center gap-3 border-b border-border border-l-2 border-l-brand bg-brand/5 px-4 py-1.5">
+      <span className="inline-flex shrink-0 items-center gap-1.5">
+        <AgentMark className="h-3 w-3 text-brand" />
+        <span className="font-mono text-[10px] font-semibold uppercase tracking-wide text-brand">
+          {"AGENT'S READ"}
+        </span>
+      </span>
+
+      {intent !== null ? (
+        <span
+          className="min-w-0 flex-1 truncate text-xs text-muted-foreground"
+          title={stripMarkdown(intent)}
+        >
+          {previewText(intent)}
+        </span>
+      ) : (
+        // No intent yet — keep the flex spacer so the chips + link stay right-aligned.
+        <span className="min-w-0 flex-1" />
+      )}
+
+      {chips.length > 0 && (
+        <span className="flex shrink-0 items-center gap-2.5 font-mono text-[10px] tabular-nums">
+          {chips.map((c) => (
+            <span
+              key={c.meta.short}
+              className="inline-flex items-center gap-1"
+              title={`${String(c.count)} ${c.meta.label} finding${
+                c.count === 1 ? "" : "s"
+              }`}
+            >
+              <span
+                className={cn("h-1.5 w-1.5 shrink-0 rounded-full", c.meta.dot)}
+                aria-hidden="true"
+              />
+              <span className="text-foreground">{String(c.count)}</span>
+              <span className={c.meta.text}>{c.meta.short}</span>
+            </span>
+          ))}
+        </span>
+      )}
+
+      <button
+        type="button"
+        onClick={onOpenBriefing}
+        className="inline-flex shrink-0 cursor-pointer items-center gap-0.5 border-none bg-transparent p-0 font-mono text-[10px] font-semibold uppercase tracking-wide text-brand hover:underline"
+        title="Open the Briefing tab"
+      >
+        Briefing
+        <ArrowUpRight className="h-3 w-3" />
+      </button>
+    </div>
+  );
+}