feat(harness): thinking default-collapsed preference toggle via Leader+t (plan #742)

[btipling]

Thinking default-collapsed preference (Leader + t) — plan #742

A harness preference thinking default = collapsed, ON by default, toggled by a
keyboard shortcut (Leader Ctrl+Shift+Space, then t), registered on the parent
keymap (#741). When ON, thinking rows stay collapsed even during the active Busy
turn unless the operator expands one; when OFF, today's Busy pin is restored.

Change (Zig + docs only)

• thinking_collapse.zig — shouldRenderFull now takes the preference as an
  explicit boolean parameter (default_collapsed); the module stays pure
  (imports nothing). Policy: full iff operator_open OR (NOT default_collapsed AND active_turn_full) — the Busy pin is relaxed when default-collapsed is ON.
• ui/state.zig — thinking_default_collapsed: bool = true, reset to ON in
  resetTranscriptScroll().
• ui/thinking.zig — threads the live preference into the policy; the
  is_active pin is gated (active rows stay pinned only when the preference is
  OFF), and active-row clicks route through thinking_open_l1 so the operator
  can expand a row mid-Busy.
• keymap seams (4, plan-review resolved) — keymap.zig adds
  Action.thinking_default_toggle + a leader-pending t arm in match() (like
  the ? arm) + a KEY_TABLE row; keymap_dispatch.zig adds the
  toggleThinkingDefault handler seam + runAction arm (disarms the leader);
  help_overlay.zig adds the rowChord case (exhaustive switch, compile-forced);
  ui.zig provides the toggleThinkingDefault() seam and wires the dispatch.
• docs — docs/harness-limits.md (keyboard table + Thinking collapse row)
  and docs/agent-stream.md (qualifies the old absolute "Busy keeps thinking
  fully expanded" with the preference).

Verification

Gate	Result
zig fmt --check	clean (7 touched .zig files)
zig build test-rich	92/92 steps · 1296 tests passed (keymap 36→39, thinking_collapse 10→13)
zig build test-rich-invariants	green
zig build harness -Doptimize=Debug	full Wasm compile clean
build-harness CI	green (below)

No TS files changed → vitest/typecheck/DI-cost gates N/A (per layer rule).
Caps: none added or changed; Cloud ops N/A; no production mutate.

https://github.com/btipling/invincible — parent stack

This is a stacked PR — it must be based on the parent branch
plan/harness-keymap (PR #746, plan #741), per the plan's mandatory guard
("never implement against a main without the keymap"). The parent #746 is
still open/merge-ready, so this PR is opened against plan/harness-keymap to
keep the diff atomic to #742's delta.

Merge order: land #746 first, then rebase/retarget this PR onto main (git
automatically drops the inherited keymap delta) and re-pass adversarial review.
The single git-stack diff vs plan/harness-keymap is exactly the #742 work.

Closes #742

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
invincible	Ignored		Aug 21, 2026 7:14am

[btipling]

Implementation of plan #742 complete and merge-ready from review (Zig + docs only, no merge).

• Change: thinking default-collapsed preference on by default, toggled by Leader then t — policy (shouldRenderFull param threaded, module kept pure), ui/state.zig bool + reset, ui/thinking.zig active-pin gating + thinking_open_l1 routing, and the 4 keymap seams (match arm, Action+row, dispatcher handler, help label). Docs updated (harness-limits.md, agent-stream.md).
• Gates: zig fmt --check clean · zig build test-rich 92/92 · test-rich-invariants green · zig build harness -Doptimize=Debug clean · build-harness CI green (run 32457814854, 2m52s). No TS changed → vitest/typecheck N/A.
• Stack: based on plan/harness-keymap (parent PR feat(harness): single keymap + leader + help overlay for shortcuts (plan #741) #746, plan plan: harness keyboard shortcuts (keymap, leader, help overlay) #741) per the plan's mandatory guard. Land feat(harness): single keymap + leader + help overlay for shortcuts (plan #741) #746 first, then rebase/retarget onto main and re-pass adversarial review.

Next step: /adversarial_review #751 once parent #746 lands/coordinates.