fix(tui): load local plugins via SEA-safe import - #42485

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AI code review — automated review for reference; please use your judgment.

• packages/tui/src/plugin/context.tsx:594 — the checked annotation : { readonly default?: unknown } was replaced by an unchecked as assertion on importModule()'s return — if runtime-import's return type ever drifts (e.g. starts returning a namespace wrapper), this silently widens what reaches mod.default handling — consider a small typed wrapper in runtime-import (or a satisfies-style shape check) so the previous compile-time safety survives.
• packages/tui/src/plugin/context.tsx:591-594 — version reaching this call site comes from either the raw entrypoint or freshSpecifier(entrypoint, generation), so its form (plain path, file:// URL, bare/package specifier) varies — please confirm importModule falls back to native import() for every one of those forms so behavior outside SEA builds stays byte-identical to the old await import(version).
• packages/tui/src/plugin/context.tsx:594-604 — native import() failures carry recognizable error types/messages and the surrounding retry logic keys off import failures — verify importModule re-throws with equivalent error shapes rather than swallowing/wrapping them, otherwise the generation-retry path may mis-classify failures.
• packages/tui/test — no test covers plugin loading through importModule under the SEA/bundled runtime this change targets — a single integration test that loads a fixture plugin through this path would pin the exact regression class this PR fixes.
• nit — packages/tui/src/plugin/context.tsx:594 — a one-line comment stating why raw await import() is unsuitable here (SEA dynamic-import semantics) would spare future readers re-deriving the reason.

— AI code review (automated)

fixed in #46901