fix(tui): close frame coalescing lifecycle gaps

packages/agent/changelog.d/5321-frame-coalescing-lifecycle.md

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+### Fixed
+
+- Successor, terminal-error, and forced-abort handling now wait for an in-flight published `turn_end` checkpoint consumer before admitting later work or publishing `agent_end`, preventing canonical repeat-rule state from lagging behind terminal lifecycle changes. Tool calls cancelled after their pre-dispatch hook now invoke the cleanup hook exactly once with the authoritative cancellation result.
+- External lifecycle emitters now pass a session-owned admission fence before mutating Agent state. Run-bound terminals retain their authoritative attempt scope, while Cursor-native lifecycle emitters resolve the current main-attempt scope on every emission so in-loop retries and later tool turns are not mistaken for retired producers.
+- Provider iterators that close with a trailing assistant but no explicit `done`/`error` event now publish the canonical `message_end` before `turn_end` and `agent_end`, preventing session persistence from missing the authoritative final response.
+- Provider stream cancellation keeps one signal listener, bounds per-read abort-race reactions, and observes synchronous aborts raised inside provider factories.
+- Lossless degraded snapshots preserve only validated, size-bounded transport codes, retry headers, and HTTP/2 diagnostics while dropping unreadable, oversized, or non-cloneable values.
+- Normal Agent requests now retain provider-visible prompt-prefix telemetry, and `Agent.reset()` starts a fresh cache lineage.