install_log_buffer

Attach the in-memory buffer handler to target (idempotent).

Lowers target's level to at most INFO so the console shows a useful tail even when DEEPAGENTS_CODE_DEBUG is off; never raises the level. In __init__.py this runs before configure_debug_logging, which then sets the final level (honoring DEEPAGENTS_CODE_DEBUG and DEEPAGENTS_CODE_LOG_LEVEL) over this INFO floor — so any startup warnings configure_debug_logging emits are captured by the already-installed buffer. On a fresh NOTSET logger the NOTSET branch forces INFO without consulting DEEPAGENTS_CODE_LOG_LEVEL; the > INFO and no env branch only matters on reconfiguration (e.g. an importlib.reload), where it preserves an explicit DEEPAGENTS_CODE_LOG_LEVEL rather than clobbering it with INFO.

Lowering the level does not spill log output onto the terminal: because this handler is present in the propagation chain, Logger.callHandlers finds a handler (found > 0) and Python's lastResort stderr handler is never consulted. The exception is an embedding process that attaches its own INFO-or-lower handler to the root logger, which would then see the propagated records.

Note: this runs as an import-time side effect (see __init__.py), so every import deepagents_code attaches the handler and may lower the package logger's level to INFO for the lifetime of the process.