#104 #98 sanitize_output returns Cow + VecDeque grid for O(1) scroll

[kirich1409]

Summary

• Session read_loop: two allocations per PTY read — use Cow for sanitize #104 (Cow): `sanitize_output` allocated a `Vec` on every PTY read even when nothing was removed (no OSC-52 sequences). Changed return type to `Cow<'_, [u8]>`: fast path borrows the input slice (zero allocation), slow path (OSC-52 present) returns `Cow::Owned`. `session.rs` updated: `Bytes::from(sanitized.into_owned())` avoids the second copy.
• VT parser: Vec::remove(0) in scroll_up is O(n) on hot path #98 (VecDeque): `ScreenBuffer::grid` was `Vec`, making `scroll_up` O(n) (`remove(0)` shifts all rows left) and `scroll_down` O(n) (`insert(0, ...)`). Changed `grid` to `VecDeque` — `pop_front`/`push_back` and `push_front`/`pop_back` are now O(1).

Acceptance Criteria

#104

• `sanitize_output` returns `Cow<'_, [u8]>`
• No allocation when sanitize is a no-op (test asserts `Cow::Borrowed`)
• Sanitize tests pass

#98

• `ScreenBuffer::grid` is `VecDeque`
• `scroll_up` uses `pop_front` / `push_back` (O(1))
• `scroll_down` uses `pop_back` / `push_front` (O(1))
• `insert_lines`, `delete_lines`, `resize` updated accordingly
• All 179 tests pass

Closes #104
Closes #98

[Copilot]

Pull request overview

This PR primarily targets performance on the PTY read hot path by making sanitize_output allocation-free when it’s a no-op, and updates session broadcasting to avoid an extra copy when sanitization produces an owned buffer. It also includes additional performance/test refactors in the REST layer and VT screen buffer.

Changes:

• Change vt_parser::sanitize_output to return Cow<[u8]> with a borrowed fast path and owned slow path, plus tests asserting the borrowed behavior.
• Update TerminalSession broadcasting to use Bytes::from(sanitized.into_owned()) to avoid a second copy when sanitization already allocated.
• Add Store::for_tests() and refactor multiple REST-related tests to use it; introduce cached system metrics (SysCache) in REST state.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
runner/src/vt_parser.rs	sanitize_output now returns Cow; additional ScreenBuffer storage/scrolling changes.
runner/src/session.rs	Broadcast path updated to leverage Cow and avoid extra allocations/copies.
runner/src/store.rs	Adds Store::for_tests() helper for in-memory SQLite + migrations.
runner/src/rest_handlers/sessions.rs	Test helpers updated to use Store::for_tests() and new AppState.sys_cache.
runner/src/rest_api.rs	Adds SysCache with TTL and threads it through AppState; refactors health/metrics to use the cache; test updates.
runner/src/main.rs	Wires sys_cache into the production AppState initialization.

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