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/lib/lane-agents.js

@@ -1,6 +1,6 @@
 /**
- * @file Installs a lane's driving instructions. For a `claude` lane that is
- * the ship-feature-lane pipeline's agent templates
+ * @file Installs a `claude` lane's driving instructions: the
+ * ship-feature-lane pipeline's agent templates
  * (qc-local, senior-gate-reviewer) into a lane's own .claude/agents/, so a
  * driving session can launch them by the BARE subagent_type name. Source is
  * the repo's own `agents/` — the same files the agenthub plugin ships, where
@@ -20,50 +20,36 @@ const TEMPLATE_DIR = path.join(__dirname, "..", "..", "agents");
 const TEMPLATE_FILES = ["qc-local.md", "senior-gate-reviewer.md"];
 const EXCLUDE_LINE = ".claude/agents/";
 
-// Codex reads no `.claude/agents/`, so for a codex lane the useful thing to
-// install is the one instruction it DOES read: AGENTS.md, the project doc it
-// loads from the working directory. Marker-delimited so a reinstall replaces
-// exactly this block and never the user's own prose, and appended rather than
-// written over an existing file.
+// The block older builds wrote into a codex lane's AGENTS.md. Codex lanes no
+// longer carry a pipeline, so `removeStageDoc` takes it back out.
 const STAGE_BLOCK_START = "<!-- agenthub:stage:start -->";
 const STAGE_BLOCK_END = "<!-- agenthub:stage:end -->";
-const STAGE_BLOCK = `${STAGE_BLOCK_START}
-## Declare your lane stage as you work
 
-This directory is watched by AgentHub. Its pipeline map advances on its own by
-*inferring* your stage from your tool calls, but an inference carries no
-evidence — the node stays amber, never green. Only your own declaration does:
-
-\`\`\`bash
-agenthub stage <stage> --tool codex --evidence "<what is actually done>"
-\`\`\`
-
-- Call it at every real transition — starting to plan, starting to implement,
-  running tests, opening the PR — not once at the end.
-- \`--tool codex\` matters: one directory can back both a \`claude\` lane and a
-  \`codex\` lane, and without a tool the command fails rather than guess. Inside
-  a pane the dashboard started you need nothing — it carries \`AGENTHUB_LANE_ID\`.
-- \`agenthub stage\` warns on stderr and names the valid nodes if a stage matches
-  none of this lane's pipeline template.
-- If it reports that no lane owns this directory, skip the stage calls and
-  carry on. Stage reporting is reporting, never control flow.
-- A one-line \`[agenthub]\` reminder may be typed straight into this pane asking for
-  evidence on the current stage. That is the dashboard, not the user — treat it
-  as the same instruction as this section and make the real call.
-${STAGE_BLOCK_END}`;
-
-/** Append the stage block to `<cwd>/AGENTS.md`, or replace an existing one. */
-function installStageDoc(cwd) {
+/**
+ * Remove AgentHub's stage block from `<cwd>/AGENTS.md`, leaving every other
+ * line as it was. A file left with nothing else in it was AgentHub's own
+ * creation, so it is deleted. Never throws.
+ *
+ * @returns {boolean} whether the file changed
+ */
+function removeStageDoc(cwd) {
   const file = path.join(cwd, "AGENTS.md");
-  const existing = fs.existsSync(file) ? fs.readFileSync(file, "utf8") : "";
-  const start = existing.indexOf(STAGE_BLOCK_START);
-  const end = existing.indexOf(STAGE_BLOCK_END);
-  const next =
-    start !== -1 && end > start
-      ? existing.slice(0, start) + STAGE_BLOCK + existing.slice(end + STAGE_BLOCK_END.length)
-      : `${existing.trimEnd()}${existing.trim() ? "\n\n" : ""}${STAGE_BLOCK}\n`;
-  fs.writeFileSync(file, next);
-  return "AGENTS.md";
+  try {
+    const doc = fs.readFileSync(file, "utf8");
+    const start = doc.indexOf(STAGE_BLOCK_START);
+    const end = doc.indexOf(STAGE_BLOCK_END, start);
+    if (start === -1 || end === -1) return false;
+    const rest = (
+      doc.slice(0, start).trimEnd() +
+      "\n\n" +
+      doc.slice(end + STAGE_BLOCK_END.length).trimStart()
+    ).trim();
+    if (rest) fs.writeFileSync(file, `${rest}\n`);
+    else fs.rmSync(file);
+    return true;
+  } catch {
+    return false; // no file, or unreadable — nothing of ours to take out
+  }
 }
 
 /** The dir shared across every worktree of a repo — where info/exclude
@@ -80,8 +66,8 @@ async function commonGitDir(cwd) {
  * any existing copy — this is a reinstall, not a merge) and idempotently
  * git-exclude that directory in the shared common git dir.
  *
- * A `codex` lane gets the AGENTS.md stage block instead — Codex never reads
- * `.claude/agents/`, and its own working copy is the only channel it does read.
+ * A `codex` lane gets nothing: Codex never reads `.claude/agents/`, and codex
+ * lanes carry no pipeline to drive.
  *
  * @param {{cwd: string, tool?: string}} lane
  * @returns {Promise<{installed: string[]}>}
@@ -93,7 +79,7 @@ async function installAgents(lane) {
     });
   }
 
-  if (lane.tool === "codex") return { installed: [installStageDoc(lane.cwd)] };
+  if (lane.tool === "codex") return { installed: [] };
 
   const dest = path.join(lane.cwd, ".claude", "agents");
   fs.mkdirSync(dest, { recursive: true });
@@ -116,4 +102,4 @@ async function installAgents(lane) {
   return { installed };
 }
 
-module.exports = { installAgents };
+module.exports = { installAgents, removeStageDoc };