Snapshot tests for TUI render

Status: Open — Phase 1, no confirmation needed

Problem

The TUI has no snapshot-style regression net for the largest composite panes. The render layer has grown significantly since the original analysis:

• src/console/manager/render/editor.rs is now 3231L (was ~1682L — nearly doubled)
• src/console/manager/render/list.rs is now 2816L (was ~2069L)
• src/console/manager/render/mod.rs is now 1165L (was ~500L)
• src/console/manager/render/global_mounts.rs is now 839L (new sub-module)

No insta or other snapshot testing library exists in the dependency tree. All render testing uses manual TestBackend + assert! assertions against buffer contents.

Three target functions (updated from original)

Function	File	What to snapshot
render_sentinel_description_pane	src/console/manager/render/list.rs	Static ”+ New workspace” panel. Zero state. 80×10 terminal.
render_tab_strip	src/console/manager/render/editor.rs	Tab bar with EditorTab active. 4 variants × 1 snapshot each. 80×3 terminal.
render_mounts_subpanel	src/console/manager/render/list.rs	Mount list subpanel. 3 cases: empty, 1 mount, 3 mounts. 60×20 terminal.

Additional high-value targets identified in re-analysis:

Function	File	What to snapshot
Global mounts editor rendering	src/console/manager/render/global_mounts.rs	Per-subtab renders. New 839L file with no snapshot coverage.
Per-tab editor body renders	src/console/manager/render/editor.rs	At minimum: General, Mounts, Agents, Secrets tab body renders.
Workspace list renders	src/console/manager/render/list.rs	Active workspace detail panel with various mount configurations.

Implementation

Use insta for snapshot storage + review workflow; ratatui::backend::TestBackend for the buffer (already used widely in existing tests — no extra dependency just for the backend).

Library	Stars	Approach	Fit
insta	~4k	String snapshots with cargo insta review	Best — simple, no async, inline or file-based
ratatui::backend::TestBackend	built-in	Raw buffer comparison	Already available
trycmd	~400	CLI snapshot testing	Wrong layer — tests full CLI, not render functions

Steps

1. Add insta to [dev-dependencies] in Cargo.toml.
2. Write test modules using TestBackend + insta::assert_snapshot!(). Start with the 3 original targets, then add the new targets.
3. Run cargo insta review to accept the initial snapshots.
4. cargo nextest run already runs snapshot comparisons — no additional CI step needed.

Why before Phase 2

These snapshot tests are the regression net for the Phase 2 file splits AND the Phase 1.5 DRY extractions. The TUI render layer has extreme boilerplate duplication (120 Style::default() chains, 18 Block::default() constructions, 192 Span constructions) — snapshot tests make it safe to extract shared helpers without silently changing TUI appearance.