Struct Fx 

pub struct Fx<'a> {
    pub driver_target: PathBuf,
    pub adapter_target: Option<PathBuf>,
    pub editor: &'a dyn Fn(&Path) -> Result<()>,
    pub tool_stdin: &'a mut dyn Read,
    pub tool_stdout: &'a mut dyn Write,
    pub tool_stderr: &'a mut dyn Write,
    pub stop: &'a AtomicBool,
    pub tool_injection: Option<&'a dyn ToolInjection>,
}

The binding’s injections (ARCH §3.4 “Process effects stay at the binding”). Every process-global or terminal effect a verb needs is a field here, supplied by the binding — the library reaches for none of its own.

Fields

driver_target: PathBuf

The re-entry path for every seam that goes back through the front door: the detached litany advance launch and the §6 successor execve (§2.11), the §3.3 tool resolver’s third hop (<driver_target> tool <name>), and the dispatch / message built-ins’ own re-entry. ARCH §2.11: “the driver target is injected at the binding, not resolved by name” — the exec binding resolves it once via std::env::current_exe, a linked host names its own re-exec target or a PATH-resolved litany. The library resolves none of its own.

adapter_target: Option<PathBuf>

The provider-adapter target (ARCH §4.4), injected the same way as Self::driver_target: the library resolves no binary of its own, the binding names it. None — the exec binding’s default — leaves today’s resolution intact (the models.yaml adapter: override, else bz on PATH, §4.2). An embedding host that re-execs itself as the adapter names its own target here; like an explicit override, a named target skips the load-time version guard and the in-band MessageStart.v handshake governs (§4.4).

editor: &'a dyn Fn(&Path) -> Result<()>

The litany config $EDITOR hand-off (§2.2) — the interactive spawn the exec binding supplies as cli::edit_in_editor.

tool_stdin: &'a mut dyn Read

The litany tool stdin (§3.3 tool_use.input JSON).

tool_stdout: &'a mut dyn Write

The litany tool stdout (§3.3 raw result bytes).

tool_stderr: &'a mut dyn Write

The litany tool stderr (§3.3 stderr-concat contract).

stop: &'a AtomicBool

The executor’s SIGTERM flag (§2.9 step 3), the driver verbs’ Deps::stop. The exec binding wires prelude::stop_flag after prelude::install_stop_handler.

tool_injection: Option<&'a dyn ToolInjection>

The binding’s tool injection (ARCH §3.3 Host-injected tools), injected like Self::driver_target, and its one choice of execution pipeline: None (the exec binding) spawns every tool through the §3.3 three hops; a host supplying one has its ToolInjection::tools declared and permitted on every request and its ToolInjection::route answering every invocation, with no resolution behind it. ToolInjection, DESIGN_TOOL_INJECTION §3.4.