GeezerVison

PaneObservation.capture(pane) retains sampled pane text after redraw or removal. It copies lines and the actual command argv into a frozen standalone value, retaining capture selection and the controller's monotonic interval without live pane/server references.

The call uses the supplied pane.cmd route and refuses failed or oversized captures instead of returning a successful empty value. The decoded-text admission limit counts Python Unicode code points and LF, after the existing transport returns. It is not a transport memory cap or an added deadline. Pane lifetime remains explicitly unknown with the legacy handle. Lines are frozen before their retained size is measured, so a backend mutation cannot bypass the decoded-text admission check.

For example, saved = PaneObservation.capture(pane, start=-20) retains saved.text and saved.command after redraw or removal. Its range and joined-line selection follow tmux 3.2a capture semantics.

This is the independent pane-value slice of #370 and #584 under #629, based on current master with sibling branches absent. PR #568 still retains mutable nested lists/dicts; #587/#590 cover inherited object graphs and #613 covers mutable ASCII rendering and pytest integration. Their wider work remains open. This slice adds no engine classes, object graph, serializer or persistent recording.

Validation:

• Owned noninteractive producer and API example on connected tmux 3.2a, 3.7b and stable 3.8; all retained fields survive redraw, pane removal and server destruction.
• Actual custom command routing to a live selected endpoint despite a different facade endpoint; immutable text/argv aliases, Unicode/LF admission, native oversized captures, missing resources, stderr/nonzero/unknown status and original backend errors.
• The original size-admission defect fails before repair; deliberate mutations of immutability, output ownership, routing, capture errors and limit enforcement fail their corresponding regressions.
• Historical proposed-engine composition routed to the selected borrowed engine; that earlier receipt has not been requalified on this candidate.
• Historical disposable composition with PR command(feat[timeout]) Add opt-in per-call deadlines #807 remains recorded; current qualification builds each slice independently.
• Ruff, full-tree mypy, a typed external consumer, doctests, just build-docs and rendered API/changelog links pass.
• Full configured pytest on stable 3.8 is FAIL: the failing node set exactly matches unchanged master. PR tmux(fix[3.8]): Support hooks and terminal fixtures #825 separately addresses the hooks, popup and floating-pane failures; retries are disabled.
• Hosted checks at 398322f0e7442b37968add264157f15a621bd363 remain FAIL: tmux 3.3a pass; 3.2a, 3.4, 3.5, 3.6, 3.7a, 3.7b fail. CodeQL passes; codecov/project fails. The development-tmux job allows failures and is not full-suite pass evidence. The 3.2a failure is the existing capture test accepting an echoed, unexecuted completion marker; the other stable failures include the cached-binary ABI problem tracked in tmux(fix[3.8]): Support hooks and terminal fixtures #825.

Retained values remain readable while referenced, including after server loss; process exit loses the in-memory value. Captures cannot establish omitted-output continuity, hidden terminal state, or arbitrary-shell completion. A cooperating producer's signal establishes only its application-defined milestone. No macOS work or minimum-version change is included; existing support remains unchanged.

Refs #370 and #584. Keep full object graphs, serialization and wiring retained observations into every failure open under those canonical issues. The failed mandatory full-suite gate keeps delivery partial; maintainer review remains pending.