fix: restore Go signup prompts and stop free-tier retries

[opencode-agent]

Summary

• Treat FreeUsageLimitError as exhausted free-tier quota, not a transient 429. Stop after the first failed attempt, including when retry headers are present; ordinary rate-limit retries are unchanged.
• Preserve a dedicated provider.free-tier-limit session error with the Go signup URL.
• Restore the App's Go signup dialog using V2's server-wide session.execution.failed event, retaining localization and the Go connection flow.
• Restore the TUI's original animated Go modal: expanding rings, shimmering logo, Subscribe, keyboard/pointer navigation, the 24-hour cooldown, and persistent “Don't show again.” Use V2's semantic theme colors and respect animations: false with static art.
• Keep background-session errors and existing dialogs from interrupting the current UI. Escape starts a cooldown without opting out; Subscribe opens https://opencode.ai/go.

Comparison with dev

packages/opencode/src/session/retry.ts recognized FreeUsageLimitError and attached a Go upsell action to retry status. Both the App and V1 TUI consumed that legacy session.status action; the TUI displayed DialogRetryAction with BgPulse. V2 lost that path and classified the error as retryable.

This restores both signup modals without restoring the retries. Execution failures are process-global, so the listeners accept server-wide events without a location envelope. The animation's original drawing math and logo come from dev at 79d503150ca22f151afe4ea543fac8a8eb8aef53.

Animation performance

Reviewed OpenTUI's FrameBufferRenderable, OptimizedBuffer, render-command reuse, renderer scheduling, and native framebuffer-copy paths before adapting the animation:

• One persistent opaque native framebuffer; no per-cell Solid/text work or extra buffered layer.
• Geometry and glyph templates change only with geometry/color capability. Lazily cache the original 138 animation phases instead of painting an unused warm-up frame plus the displayed frame.
• Cached phases use typed-array color copies; unchanged phases skip writes.
• A component-owned 30 Hz OpenTUI SystemClock timer requests frames with live: false. It does not change the application's FPS or force a permanently live render tree. Hidden art requests no frames; disabled/unmounted art clears its timer.

Five-sample native-buffer microbenchmark, Bun 1.3.14 / OpenTUI 0.5.10 on Linux:

• 60×16 RGB: cold paint 94.66 → 54.91 µs/frame (42% lower); cached paint 0.39 µs/frame.
• 116×20 RGB: cold paint 160.04 → 92.67 µs/frame (42% lower); cached paint 0.93 µs/frame.
• All 138 phases matched the original uncached V1 painter across both sizes and RGB modes, comparing characters, attributes, foreground and background channels—including cache revisits.

These are painter-only timings, not an end-to-end terminal CPU claim.

Validation

• AI error/executor/schema tests: 72 passed.
• Core session-runner/error/AI SDK tests: 233 passed across scoped runs; the 194 session/error tests were also rerun after the modal follow-up.
• App usage-exceeded unit tests: 2 passed. Four browser tests passed across three repetitions (12/12, no retries).
• TUI animation and Go-modal suites: 21 passed; including adjacent dialog suites: 47 passed, 1,267 assertions. Covers palette/geometry invalidation, exact phase boundaries, hidden/disabled/unmount behavior, unchanged renderer FPS, 40/100-column layout, Tab/Shift+Tab, browser opening, and dismissal persistence.
• AI/Core/App/TUI typechecks, App E2E typecheck, formatting, scoped lint, and diff checks passed.
• Recorded the actual V2 TUI with Terminal Control and an isolated local HTTP 429 fixture. Earlier App desktop/mobile and TUI light/dark coverage is retained.
• Production-build App session-entry benchmark: all 3 post-change scenarios passed. The initial baseline had one navigation timeout, so no App performance improvement is claimed.

Requested by: @thdxr (dax via Slack); animation requested by @kitlangton (Kit via Slack)