fix(tui): restore skill turns through undo and redo #48484

Outcome

TUI /undo, the undo shortcut, message Revert, and /redo correctly stage, advance, and clear rollback state for canonical Session V2 turns containing structured $skill mentions. Restored composer input preserves the structured mention when the exact Skill is still available and reports the existing actionable error when it is not.

Governing RFC

RFC-0012, especially “$skill structured mention” and its requirement that undo/history restore rebuild or remove the bound extmark. This is a bug fix restoring accepted behavior, not a new product decision.

In scope

• Route undo/redo to Session V2 revert APIs when the rollback boundary is a canonical message.
• Read canonical revert state consistently for command availability and execution.
• Restore structured skill/file/agent prompt state through the canonical restoration path.
• Preserve legacy undo/redo behavior for legacy-only turns.
• Add regression coverage for canonical skill undo/redo routing and prompt restoration.

Out of scope

• Changing Session V2 revert semantics or durable schemas.
• Changing Skill catalog admission or snapshot format.
• Migrating all ordinary TUI prompts from the legacy Session API.
• Changing Web/Desktop behavior.

Dependencies

None.

Contracts and likely areas

• packages/tui/src/routes/session/index.tsx
• packages/tui/src/routes/session/dialog-message.tsx
• packages/tui/src/util/session-message.ts
• TUI command/session tests
• Existing Session V2 revert.stage, revert.clear, and revert.commit contracts remain unchanged.

Acceptance checks

• Undoing the newest canonical $skill user turn stages its canonical message ID and restores the structured Skill mention in the composer.
• Repeated undo advances to the preceding user boundary without crossing storage models incorrectly.
• Redo uses canonical staged state and either advances the boundary or clears it at the end.
• A canonical Skill no longer available in the active catalog produces the existing actionable error and does not stage a revert.
• Legacy-only turns retain existing undo/redo behavior.
• Failures are surfaced instead of becoming successful no-ops.

Verification

• Package-local TUI unit tests and typecheck.
• Relevant Core Session V2 revert tests.
• Mac real-device TUI: create a temporary Session, submit a $skill turn, exercise message Revert, /undo, repeated undo, and /redo; capture screenshot/log evidence.
• mywindows/WSL2 real-device TUI through opencode-rexd: repeat the same temporary Session scenario against the same commit; capture screenshot/log evidence.

Risks and compatibility

• Incorrect V1/V2 routing could delete or hide the wrong transcript boundary; tests must cover mixed legacy/canonical timelines and repeated undo/redo.
• Composer reconstruction must never expose embedded Skill instruction bodies.
• No generated API/SDK artifacts are expected.