feat: per-change-block hunk actions (#50), codex lanes without a pipeline, macOS LaunchAgent

- git (#50): stage-hunk/discard-hunk take an optional `block` — one run of
  consecutive +/- lines inside an @@ hunk. `onlyBlock` (server/lib/git-diff.js)
  cuts git's fresh hunk down to it, folding the other blocks into the side
  being checked; LaneDiffView hangs one review bar per block (unified + split)
  and its arrows walk blocks.
- git exclude: entries AgentHub writes for a lane go to the COMMON git dir with
  the lane's path prefix (server/lib/git-exclude.js, used by router-apply and
  lane-mcp) — a linked worktree's own info/exclude is never read by git, and a
  subdir lane has no .git. MCP sync no longer fails with ENOTDIR on a worktree
  lane or creates a stray .git in a non-repo lane.
- codex lanes carry no pipeline: codex-ingest mirrors only idle/running,
  codex-nudge is removed, agents install writes nothing for codex, the
  Workspace hides stage/pipeline/feature pickers/PipelineMap for them, and
  every server start clears leftover codex stage data and the old AGENTS.md
  stage block.
- Changes panel: a whole file opens for reading and enters the editor on a
  click on its text (caret at the clicked line), not automatically.
- macOS: LaunchAgent start-at-login (scripts/launchd-service.js, picked by
  scripts/service-manager.js).
- Adds the AgentHub introduction slides and their image-embedding script.

server/__tests__/lane-agents.test.js

@@ -18,7 +18,7 @@ const { describe, it, after } = require("node:test");
 const assert = require("node:assert/strict");
 
 const lanesLib = require("../lib/lanes");
-const { installAgents } = require("../lib/lane-agents");
+const { installAgents, removeStageDoc } = require("../lib/lane-agents");
 
 after(() => fs.rmSync(SUITE_ROOT, { recursive: true, force: true }));
 
@@ -116,29 +116,77 @@ describe("installAgents", () => {
     assert.ok(fs.existsSync(path.join(cwd, ".claude", "agents")));
   });
 
-  it("installs the AGENTS.md stage block for a codex lane, not .claude/agents/", async () => {
+  it("installs nothing for a codex lane — no .claude/agents/, no AGENTS.md", async () => {
     const cwd = makeRepoDir();
     const lane = lanesLib.createLane({ title: "cx", cwd, kind: "managed", tool: "codex" });
 
     const result = await installAgents(lane);
-    assert.deepEqual(result.installed, ["AGENTS.md"]);
+    assert.deepEqual(result.installed, []);
     assert.equal(fs.existsSync(path.join(cwd, ".claude", "agents")), false);
-    const doc = fs.readFileSync(path.join(cwd, "AGENTS.md"), "utf8");
-    assert.match(doc, /agenthub stage <stage> --tool codex/);
-  });
-
-  it("preserves the user's own AGENTS.md prose and replaces only the block", async () => {
-    const cwd = makeRepoDir();
-    const lane = lanesLib.createLane({ title: "cx", cwd, kind: "managed", tool: "codex" });
-    const file = path.join(cwd, "AGENTS.md");
-    fs.writeFileSync(file, "# House rules\n\nNever force-push.\n");
-
-    await installAgents(lane);
-    await installAgents(lane); // reinstall must not duplicate the block
-
-    const doc = fs.readFileSync(file, "utf8");
-    assert.match(doc, /Never force-push\./);
-    assert.equal(doc.split("<!-- agenthub:stage:start -->").length - 1, 1);
-    assert.equal(doc.split("<!-- agenthub:stage:end -->").length - 1, 1);
+    assert.equal(fs.existsSync(path.join(cwd, "AGENTS.md")), false);
+  });
+});
+
+describe("codex pipeline cleanup", () => {
+  const START = "<!-- agenthub:stage:start -->";
+  const END = "<!-- agenthub:stage:end -->";
+  const BLOCK = `${START}\n## Declare your lane stage as you work\n\nagenthub stage …\n${END}\n`;
+
+  it("removes only the AgentHub block, keeping the user's own AGENTS.md prose", () => {
+    const cwd = makeRepoDir();
+    const file = path.join(cwd, "AGENTS.md");
+    fs.writeFileSync(file, `# House rules\n\nNever force-push.\n\n${BLOCK}\n## More\n\nKeep me.\n`);
+
+    assert.equal(removeStageDoc(cwd), true);
+    const doc = fs.readFileSync(file, "utf8");
+    assert.ok(!doc.includes(START) && !doc.includes(END));
+    assert.match(doc, /Never force-push\./);
+    assert.match(doc, /Keep me\./);
+  });
+
+  it("deletes an AGENTS.md that held nothing but the block", () => {
+    const cwd = makeRepoDir();
+    fs.writeFileSync(path.join(cwd, "AGENTS.md"), BLOCK);
+    assert.equal(removeStageDoc(cwd), true);
+    assert.equal(fs.existsSync(path.join(cwd, "AGENTS.md")), false);
+  });
+
+  it("leaves a file without the block, or no file at all, untouched", () => {
+    const cwd = makeRepoDir();
+    assert.equal(removeStageDoc(cwd), false);
+    fs.writeFileSync(path.join(cwd, "AGENTS.md"), "# Mine\n");
+    assert.equal(removeStageDoc(cwd), false);
+    assert.equal(fs.readFileSync(path.join(cwd, "AGENTS.md"), "utf8"), "# Mine\n");
+  });
+
+  it("wipes a codex lane's stage, detection, stage log and features — and no claude lane's", () => {
+    const codex = lanesLib.createLane({ title: "cx", cwd: makeRepoDir(), tool: "codex" });
+    const claude = lanesLib.createLane({ title: "cc", cwd: makeRepoDir(), tool: "claude" });
+    for (const lane of [codex, claude]) {
+      lanesLib.setStage(lane.id, { stage: "tests", evidence: "old" });
+      lanesLib.recordDetection(lane.id, { nodeId: "review", signal: "npm test" });
+    }
+    const { db } = require("../db");
+    const insertFeature = db.prepare("INSERT INTO lane_features (lane_id, slug) VALUES (?, ?)");
+    insertFeature.run(codex.id, "old-feature");
+    insertFeature.run(claude.id, "kept-feature");
+
+    assert.equal(lanesLib.clearCodexPipelines(), 1);
+
+    const cx = lanesLib.getLane(codex.id);
+    assert.equal(cx.stage, "idle");
+    assert.deepEqual(cx.stages, {});
+    assert.equal(cx.detected_stage, null);
+    const count = (table, id) =>
+      db.prepare(`SELECT COUNT(*) AS n FROM ${table} WHERE lane_id = ?`).get(id).n;
+    assert.equal(count("lane_stage_events", codex.id), 0);
+    assert.equal(count("lane_features", codex.id), 0);
+
+    const cc = lanesLib.getLane(claude.id);
+    assert.equal(cc.stage, "tests");
+    assert.ok(count("lane_stage_events", claude.id) > 0);
+    assert.equal(count("lane_features", claude.id), 1);
+
+    assert.equal(lanesLib.clearCodexPipelines(), 0); // idempotent
   });
 });