feat(chat): add compact-mode with sticky header and sticky user messages

[Blankeos]

Add /compact-mode command support to toggle compact layout while preserving chat-only behavior. Implement sticky session-title header and last fully-scrolled user message in compact mode with click-to-scroll, plus faded viewport copy handling and adjusted hit-testing to keep interaction and rendering stable.

I wanted to kinda copy Grok. It looked convenient.. It's toggleable by /compact-mode (also similar to Grok Build)

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View logs

[Blankeos]

PR Review: feat/sticky-message-headers → main

Merge confidence: 4/5

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Summary

Implements compact mode — a view toggle (/compact-mode or via app handler) that collapses the chat to show a narrow 3-row area with sticky user message headers above the latest assistant reply. Clicking a sticky user message bar scrolls directly to that message with hysteresis. Extends the scroll target region to include the sticky bar + header rows so wheel events work over that chrome. Adds the /compact-mode slash command.

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Diff overview

File	+/−	What changed
src/views/chat.rs	~+270	Compact-mode layout: split area into 3 chunks (prior messages / sticky bar / latest reply), sticky‑click target tracking, hysteresis logic for sticky index, compact→normal state teardown
src/app.rs	~+60	chat_scroll_region fn to include sticky bar in scroll area, mouse click handler for sticky bar, /compact-mode intercept to toggle chat_state.compact_mode
src/command/handlers.rs	+16	New /compact-mode command registration
src/ui/components/chat.rs	+1	scroll_to_message_index (possibly pre-existing unused until now)

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Issues found

⚠️ 1. Registry test not updated — will fail CI

src/command/handlers.rs:1392 asserts names.len() == 19, but the new compact-mode command makes it 20. The test also doesn't verify the new command at all.

Fix: bump to 20 and add assertions for compact-mode (name + is_chat_only).

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Regressions

None. The compact mode is opt-in (defaults off) and adds no branching to the normal render path beyond the early if self.chat_state.compact_mode check at src/views/chat.rs:78. All existing tests pass except the pre-existing question_dialog oserror failures.

Test suite	Result
cargo build	✅ clean
cargo fmt --check	✅ clean
cargo test views::chat	✅ all pass
cargo test app::tests	✅ all pass
cargo test ui::components::chat	✅ all pass
cargo test command::handlers	❌ 1 fail (test not updated — see #1)

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Migration / checklists

No DB schema or data migrations needed. No config format changes.

Pre-merge checklist

• Fix test_registry_has_all_commands: bump expected count to 20, add compact-mode to the assertions list
• Run just fmt after the fix
• (Nice to have) Add a dedicated unit/integration test for compact mode toggle and sticky message rendering