feat(tui): todos pane open by default (+show-todo-pane config) with safe focus UX

[Emasoft]

Update 2026-09-25

New since the original description (b148100): the todos pane now also releases focus on any printable key that arrives as a multi-rune sequence. Dead-key and combining-character input (e.g. e + combining acute) is delivered as a single event carrying multiple runes, and the old len(runes)==1 check missed it — so those sequences kept holding focus. Focus now releases on the first printable non-control rune, so dead-key/combining input falls through to the input like any other key.

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The todos pane now starts open — and focusing it can no longer trap your typing.

• Open by default. config.json "show-todo-pane": false restores closed-at-start. Under 85 columns the pane stays closed (silently — the width guard exists to keep narrow terminals usable, not to nag).
• Focus is visible. A focused pane gets a background/border change and a [focused · esc to unfocus] marker, so you can always tell where your keys are going.
• No typing trap. While focused, the first printable non-nav key releases focus and falls through — the same keypress lands in the input. The pane can never silently swallow j/k/g.
• Mouse escape hatch. Click inside the pane to focus it, click anywhere outside to release focus.
• Unfocused = inert. When not focused, the pane provably consumes no keys: routing regression tests assert nav keys and plain keys land in the input.

New config key: show-todo-pane (bool, default true).

Split out of #133 (TUI changes evaluated separately, per review).

Testing

$ go test ./... -race -count=1
ok  	late/cmd/late	2.800s
?   	late/cmd/mcp-run	[no test files]
ok  	late/internal/agent	1.451s
?   	late/internal/assets	[no test files]
ok  	late/internal/client	2.346s
ok  	late/internal/common	4.156s
ok  	late/internal/config	1.641s
ok  	late/internal/executor	11.817s
ok  	late/internal/git	3.908s
ok  	late/internal/mcp	3.230s
ok  	late/internal/orchestrator	5.460s
?   	late/internal/pathutil	[no test files]
ok  	late/internal/plugin	14.308s
ok  	late/internal/session	1.962s
ok  	late/internal/skill	4.950s
ok  	late/internal/tool	4.589s
ok  	late/internal/tool/ast	5.160s
ok  	late/internal/tui	11.032s

exit 0 — all 18 packages green (15 ok, 3 without test files).

• gofmt -l on the touched files: no output (clean)
• go vet ./cmd/late ./internal/config ./internal/tui: clean
• New tests: startup default + /todo toggle + silent width guard (todo_pane_test.go), focus rendering/marker/background (todo_pane_test.go), unfocused pane passes keys through, printable-key release-and-fall-through, click-in/click-out focus (todo_routing_test.go)