fix(build): feature-gate serde_json out of slim build

serde_json was unconditionally included but only used for
`wallhack peers --json`. Gate behind `json` feature (included in
default, excluded from slim). Saves ~47KB in slim binary.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: maxholman

crates/cli/Cargo.toml

@@ -12,7 +12,8 @@ name = "wallhackctl"
 path = "src/bin/wallhack.rs"
 
 [features]
-default = ["quic", "websocket", "http-api", "repl"]
+default = ["quic", "websocket", "http-api", "repl", "json"]
+json = ["dep:serde_json"]
 slim = ["quic", "websocket"]
 
 # Transport features (forwarded to wallhackd)
@@ -30,7 +31,7 @@ repl = ["dep:reedline", "dep:nu-ansi-term"]
 argh = "0.1"
 prost = "0.13"
 serde = { version = "1", features = ["derive"] }
-serde_json = "1"
+serde_json = { version = "1", optional = true }
 wallhack-ipc = { path = "../ipc" }
 rand = { version = "0.9", default-features = false, features = ["std", "std_rng"] }
 # Already a transitive dep via reedline — no additional binary cost.

crates/cli/src/bin/wallhack.rs

@@ -309,6 +309,7 @@ async fn run_ctl_async(cli: wallhack_cli::cli::Cli) -> Result<(), output::CtlErr
         }),
         CtlCommand::Info(_) => management_request::Request::Status(StatusRequest {}),
         CtlCommand::Stats(_) => management_request::Request::Stats(StatsRequest {}),
+        #[cfg(feature = "json")]
         CtlCommand::Peers(ref cmd) if cmd.json => {
             // JSON output: make the request and short-circuit the standard response path.
             let request = management_request::Request::Peers(PeersRequest {});

crates/cli/src/output.rs

@@ -3,9 +3,10 @@
 use std::io::Write;
 
 use tabwriter::TabWriter;
-use wallhack_wire::management::{
-    ManagementResponse, PeerInfo as WirePeerInfo, management_response,
-};
+use wallhack_wire::management::{ManagementResponse, management_response};
+
+#[cfg(feature = "json")]
+use wallhack_wire::management::PeerInfo as WirePeerInfo;
 
 #[cfg(feature = "repl")]
 use {
@@ -15,6 +16,7 @@ use {
 
 use crate::ipc::IpcError;
 
+#[cfg(feature = "json")]
 #[derive(serde::Serialize)]
 struct PeerJson<'a> {
     name: &'a str,
@@ -50,6 +52,7 @@ fn format_uptime(ms: u64) -> String {
 /// Print the peers list as JSON to stdout.
 ///
 /// Shape matches the REST API `/peers` response plus a `tun_name` field.
+#[cfg(feature = "json")]
 pub fn print_peers_json(peers: &[WirePeerInfo]) {
     let items: Vec<PeerJson<'_>> = peers
         .iter()