fix(slash): preserve /compact ordering and resume state

[hakula139]

Summary

Hardens /compact after review so compact boundaries flush before queued writes, summarization keeps every streamed text fragment, and resume reconstructs the compact tail without replaying stale pre-compact messages.

The pass also normalizes prompt / comment prose around instruction text, removes avoidable lint suppressions through smaller helpers, and tightens shared TUI rendering code that the compact block depends on.

Design decisions

• Make compact a session-writer barrier. SessionCmd::Compact now forces the actor batch to flush before later queued commands run, so prompts typed during compaction cannot share the same buffered write after the boundary.
• Load compact entries as generation boundaries. The store keeps CompactInfo for resume display, resets sidecars at the boundary, and only accepts messages from the new compact tail. This preserves archival JSONL while keeping the active replay chain compact-aware.
• Collect stream start-frame text. Compaction now reads text from both content_block_start and content_block_delta, matching the wire protocol rather than assuming all text arrives as deltas.
• Prefer small refactors over lint suppressions. The loader state, app constructor, shared bar prefix, and checked dimension casts remove local #[expect] use where the code was reducible.

Changes

File	Description
agent/compaction.rs	Collect start-frame text, use raw strings for escaped block-kind checks, tighten the stripped request shape, and normalize compaction instructions.
session/actor.rs, session/state.rs, session/handle.rs	Treat compact as a flush barrier, keep compact state changes transactional, and trim comments to the invariants worth keeping.
session/entry.rs, session/store.rs	Add CompactInfo, load compact boundaries explicitly, filter stale old-chain writes, and extract the compact-aware loader builder.
agent/event.rs, main.rs, tui/app.rs, tui/components/chat.rs	Carry compact metadata through resume and render the boundary block while hiding the synthetic root from visible chat.
tui/components/chat/blocks*, tui/components/input.rs	Share accent-bar continuation rendering and replace unchecked dimension casts with saturating conversions.
prompt/sections.rs, prompt/instructions.rs, session/title_generator.rs, slash/init.rs, docs/design/slash/compact.md	Rewrap instruction prose at the project width, remove semicolon-heavy phrasing, and align the compact design doc with current behavior.

Test plan

• cargo fmt --all --check
• cargo build
• cargo clippy --all-targets -- -D warnings: zero warnings
• cargo test: 1919 tests pass
• cargo llvm-cov --ignore-filename-regex 'main\.rs': 98.62% line coverage
• pnpm lint
• pnpm spellcheck

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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