- `ProcessTerminal` now captures a per-instance `#headless` from `isTerminalHeadless()` at construction and re-reads it in `start()`; when set, `#safeWrite`, `start`, `stop`, `drainInput`, and `setProgress` short-circuit, so frame paints, `start()` probes (OSC 11 / DA1 / kitty), the progress keepalive, stdin raw mode, SIGWINCH, and teardown escapes no longer reach a real terminal during `bun test` (previously `#safeWrite` only skipped on `!isTTY`, so an interactive terminal leaked stray boxes and probe queries).
- Gated the `emergencyTerminalRestore()` blind-restore branch and `TerminalInfo.sendNotification` on the headless flag, and guarded `setTerminalTitle`/`pushTerminalTitle`/`popTerminalTitle` in `title-generator.ts`.
- Opted the terminal-contract suites (terminal-appearance, notifications, emergency-restore-altscreen, issue-2034 write gate, process-terminal-render-harness, render-stress-harness) back into real I/O with `setTerminalHeadless(false)`, restoring on teardown.
- Added `process-terminal-headless.test.ts` asserting zero writes under a forced TTY when headless and real frame/probe output after opt-out.
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