The Plan panel used to render a blunt "No active plan" line whenever
the model hadn't called \`update_plan\` yet — even when the panel had a
goal or a cycle counter to show above it. That made the panel look
broken on every fresh session.
Per the audit posted on the issue (option 1 of three), this PR keeps
the Plan panel as the **single source of truth for the \`update_plan\`
tool's output** and drops the placeholder when the panel is fully
quiet, replacing it with a one-line hint that explains what the panel
tracks. When a goal or cycle counter is already showing above, the
empty-steps body collapses entirely so the section doesn't look
ambiguous next to populated content.
The panel's role is documented in a doc comment on
\`render_sidebar_plan\` so the next person doesn't have to re-derive it
from the issue tracker.
### What's wired
- \`render_sidebar_plan\` checks "anything above" (goal +
cycle_count) before deciding whether to emit the empty-state hint.
If either is showing, the empty steps body adds nothing.
- New \`plan_panel_empty_hint(width)\` helper composes the hint
string with proper width-aware truncation.
- New module-level doc comment explains the Plan panel's role
(update_plan output + /goal + cycle counter) and contrasts it
with Todos.
### Tests
- 3 new tests in \`tui::sidebar::tests\`:
- hint mentions \`update_plan\` and \`/goal\` so the user
understands what populates the panel
- hint truncates correctly to a 16-column sidebar without
overflowing
- regression guard: the hint never re-introduces "no active plan"
wording
### Verification
cargo fmt --all -- --check ✓
cargo clippy --workspace --all-targets --all-features --locked -- -D warnings ✓
cargo test --workspace --all-features --locked ✓ 1850 + supporting
Closes#408 (option 1 of the audit). Options 2 (merge with todos)
and 3 (move to top-row chip) remain open as v0.9.0 design candidates
once #504's right-panel work is on the table.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Hunter Bown
68ec91999b