Land staged session/MCP/chrome work + sidebar clear-J fix

This batches the in-flight [Unreleased] block from CHANGELOG.md into a
single commit. Highlights:

- Real MCP protocol layer (initialize / tools/list / tools/call) so
  vendor MCP clients can complete the handshake against the per-PID
  socket. Legacy direct-dispatch preserved for the harness.
- New mcp_injection kinds — cli_override for codex, config_env for
  opencode — joining the existing env-var and config_file paths so
  patterm can slot into more agents without touching their real
  config or auth.
- Ctrl+A/D and Ctrl+W/S focus navigation across tabs and intra-tab
  process lists, recognised in legacy / kitty CSI u / xterm
  modifyOtherKeys encodings.
- Palette macros (sw / k / sp ) and reordering so open sessions
  surface above spawn-new entries.
- Two-row tab bar, sidebar/tabbar/status chrome cache, viewport-wipe
  on agent spawn, CR-terminated orchestrator injections, and split-
  Enter PTY writes so paste-detecting TUIs see Enter as a key event.

Also fixes the bug logged in TODO: claude's Ctrl+O tool-call expansion
emits CSI 0 J, which the viewport renderer was forwarding verbatim —
wiping the sidebar to the right of the cursor and leaving the chrome
cache convinced nothing had changed. CSI 0 J and CSI 1 J are now
translated into per-row ECH sequences clamped to the viewport, same
as CSI 2 J and CSI K already were.

Agent guides (CLAUDE.md / AGENTS.md) now spell out the
TODO->CHANGELOG workflow so completed items land in the changelog
rather than as ticked entries left behind in TODO.

internal/app/tree_test.go

@@ -39,3 +39,61 @@ func childIDs(cs []*Child) []string {
 	}
 	return ids
 }
+
+func TestNextTabIDWrapsAndSkipsCurrent(t *testing.T) {
+	r1 := testChild("c1", "root1", "", StatusRunning)
+	r2 := testChild("c2", "root2", "", StatusRunning)
+	r3 := testChild("c3", "root3", "", StatusRunning)
+	children := []*Child{r1, r2, r3}
+
+	if got := nextTabID(children, "c1", +1); got != "c2" {
+		t.Fatalf("next from c1: %q", got)
+	}
+	if got := nextTabID(children, "c1", -1); got != "c3" {
+		t.Fatalf("prev from c1: %q", got)
+	}
+	if got := nextTabID(children, "c3", +1); got != "c1" {
+		t.Fatalf("wrap forward from c3: %q", got)
+	}
+}
+
+func TestNextTabIDFromSubAgentJumpsByRoot(t *testing.T) {
+	r1 := testChild("c1", "root1", "", StatusRunning)
+	r1Child := testChild("c2", "child1", "c1", StatusRunning)
+	r2 := testChild("c3", "root2", "", StatusRunning)
+	children := []*Child{r1, r1Child, r2}
+
+	// Focus is on a sub-agent of root1; Ctrl+D should jump to root2,
+	// not stay inside root1's sub-tree.
+	if got := nextTabID(children, "c2", +1); got != "c3" {
+		t.Fatalf("next from sub-agent: %q want c3", got)
+	}
+}
+
+func TestNextChildIDCyclesWithinTab(t *testing.T) {
+	r1 := testChild("c1", "root1", "", StatusRunning)
+	a := testChild("c2", "a", "c1", StatusRunning)
+	b := testChild("c3", "b", "c1", StatusRunning)
+	other := testChild("c4", "other-root", "", StatusRunning)
+	children := []*Child{r1, a, b, other}
+
+	if got := nextChildID(children, "c1", +1); got != "c2" {
+		t.Fatalf("root->first child: %q", got)
+	}
+	if got := nextChildID(children, "c2", +1); got != "c3" {
+		t.Fatalf("a->b: %q", got)
+	}
+	if got := nextChildID(children, "c3", +1); got != "c1" {
+		t.Fatalf("wrap b->root: %q", got)
+	}
+	if got := nextChildID(children, "c1", -1); got != "c3" {
+		t.Fatalf("wrap backward root->b: %q", got)
+	}
+}
+
+func TestNextChildIDNoopWhenOnlyOneProcess(t *testing.T) {
+	r := testChild("c1", "solo", "", StatusRunning)
+	if got := nextChildID([]*Child{r}, "c1", +1); got != "" {
+		t.Fatalf("expected empty when only one process in tab, got %q", got)
+	}
+}