v0.16.4

Fixed

• Turn-limit exhaustion treated as success: Agents that exhausted their turn limit (or entered a tool call loop) were silently treated as OutcomeSuccess, allowing pipelines to advance past nodes that wrote zero files. Now returns OutcomeFail so the engine routes through explicit when ctx.outcome = fail edges (or stops via strict-failure-edge when no failure edge exists).
• Loop detection produces distinct diagnostic: turn_limit_msg context key now distinguishes "agent entered tool call loop" from "agent exhausted turn limit" for clearer tracker diagnose output.

Added

• ContextKeyTurnLimitMsg constant: New pipeline.ContextKeyTurnLimitMsg context key for turn-limit and loop-detection diagnostics. Added to reservedContextKeys() for linter recognition.
• Turn-limit and loop-detection tests: 4 new handler-level tests covering fail, auto_status override, and loop detection paths.