## Why
Issue #20489 calls out that animated TUI affordances can be noisy for
screen-reader users. Codex already has `tui.animations = false` as a
reduced-motion setting, but some live activity rows render spinner-style
prefixes in that mode. These were relatively recent regressions.
We have also regressed this pattern more than once by adding new
spinner/shimmer callsites that do not think through the reduced-motion
path, so this PR adds a small guardrail while fixing the current
surfaces.
## What changed
- Omit the live status-row spinner when animations are disabled, so the
row starts with stable text like `Working (...)`.
- Render running hook headers without the spinner prefix when animations
are disabled, while preserving shimmer/spinner behavior when animations
are enabled.
- Centralize TUI activity indicators in `tui/src/motion.rs`, with
explicit reduced-motion choices for hidden prefixes, static bullets, and
plain shimmer-text fallbacks.
- Route existing spinner/shimmer callsites through the central motion
helper, including exec rows, MCP/web-search/loading rows, hook rows,
plugin loading, and onboarding loading text.
- Add a source-scan regression test that rejects direct `spinner(...)`
or `shimmer_spans(...)` usage outside the central module and primitive
definition.
- Add focused coverage that reduced-motion active exec rows are stable,
status rows start without a spinner, running hooks omit the spinner, and
MCP inventory loading stays stable.
- Update the one affected status-indicator snapshot; the existing detail
tree prefix remains unchanged.
## Verification
- `cargo test -p codex-tui`
Eric Traut