[trissim]

Summary

1 commit; 1 file, +2/-1. Physical observations can select a native CheckRoot subtype without copying the frontend lifecycle or patching a module global.

Before / after

Before: ObservedTerminalApp.copied constructs CheckRoot directly. Its fixed 200-record budget refuses the current selected history because the newest message's answered-original closure alone exceeds that budget.
After: the runner declares check_root_type: type[CheckRoot] = CheckRoot and constructs that declared type. An observation can inherit CheckRoot and override its existing finite max_records declaration. Ordinary callers retain the same type and budget.

What stays owned

CheckRoot still owns scope selection, answer closure, bounded transcript copying, private-root admission, and source preservation. ObservedTerminalApp still owns frontend setup, isolated display, startup, and retirement. No answer is trimmed to fit; an oversized selected closure still refuses. No alternate runner, global patch, or compatibility path was added.

Evidence

• Original installed failure: /home/ts/.cache/agent-scratch/pi-typed-dispatch/dispatch-installed-physical-03.log, exit1 before frontend startup, at MessageDisplayScope.history's closure bound.
• Full two-hunk diff read; AST parse succeeds; git diff --check succeeds. Native installed source trace: CheckRoot._populate passes the subtype's max_records into the existing history owner; _session retains the existing byte bound.
• Corrected installed physical observation06 completed rc0 under Core0f8dcdbe5: eight native carrier/subscription controls, actual mailbox history publication, candidate entries1→0, all subscriptions closed. Screenshot read with no probe error notifications; frontend/Xvfb both stopped gracefully with exit0 and copied-root retirement recorded. This validates the copy hook in the existing lifecycle; it is not an ACP-view/provider journey or a performance result. Artifacts: /home/ts/.cache/agent-scratch/pi-typed-dispatch/dispatch-installed-physical-06.log and matching directory. Failed epochs03–05 remain retained.

Assumed: the observing subclass chooses an appropriate finite capacity; this hook does not certify that capacity is minimal or sufficient for every future history.

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