diff --git a/crates/nono-cli/src/command_runtime.rs b/crates/nono-cli/src/command_runtime.rs
index 3806c40e1..5ead075b7 100644
--- a/crates/nono-cli/src/command_runtime.rs
+++ b/crates/nono-cli/src/command_runtime.rs
@@ -11,8 +11,7 @@ use crate::profile;
 use crate::proxy_runtime::prepare_proxy_launch_options;
 use crate::sandbox_prepare::{
     prepare_sandbox, print_allow_gpu_warning, print_allow_launch_services_warning,
-    should_auto_enable_claude_launch_services, validate_block_net_conflicts,
-    validate_external_proxy_bypass,
+    should_auto_enable_claude_launch_services, validate_proxy_conflicts,
 };
 use crate::theme;
 use nono::{CapabilitySet, NonoError, Result};
@@ -212,8 +211,7 @@ pub(crate) fn run_sandbox(mut run_args: RunArgs, silent: bool) -> Result<()> {
 
     if args.dry_run {
         let prepared = prepare_sandbox(&args, silent)?;
-        validate_block_net_conflicts(&args, &prepared)?;
-        validate_external_proxy_bypass(&args, &prepared)?;
+        validate_proxy_conflicts(&args, &prepared)?;
         if !prepared.secrets.is_empty() && !silent {
             eprintln!(
                 "  Would inject {} credential(s) as environment variables",
@@ -242,6 +240,7 @@ pub(crate) fn run_shell(args: ShellArgs, silent: bool) -> Result<()> {
 
     if args.sandbox.dry_run {
         let prepared = prepare_sandbox(&args.sandbox, silent)?;
+        validate_proxy_conflicts(&args.sandbox, &prepared)?;
         reject_run_only_sandbox_policy("shell", &args.sandbox, &prepared)?;
         if !prepared.secrets.is_empty() && !silent {
             eprintln!(
@@ -255,6 +254,7 @@ pub(crate) fn run_shell(args: ShellArgs, silent: bool) -> Result<()> {
     }
 
     let prepared = prepare_sandbox(&args.sandbox, silent)?;
+    validate_proxy_conflicts(&args.sandbox, &prepared)?;
     reject_run_only_sandbox_policy("shell", &args.sandbox, &prepared)?;
 
     if prepared.allow_launch_services_active {
@@ -420,8 +420,36 @@ pub(crate) fn run_wrap(wrap_args: WrapArgs, silent: bool) -> Result<()> {
 
 #[cfg(test)]
 mod tests {
-    use super::reject_resource_limits_under_wrap;
+    use super::{reject_resource_limits_under_wrap, run_shell};
+    use crate::cli::{SandboxArgs, ShellArgs};
     use nono::{CapabilitySet, ResourceLimits};
+    use std::path::PathBuf;
+
+    #[test]
+    fn shell_dry_run_rejects_block_net_with_upstream_proxy() {
+        let args = ShellArgs {
+            sandbox: SandboxArgs {
+                dry_run: true,
+                allow_cwd: true,
+                block_net: true,
+                external_proxy: Some("squid.corp:3128".to_string()),
+                ..SandboxArgs::default()
+            },
+            shell: Some(PathBuf::from("/bin/sh")),
+            name: None,
+            startup_timeout_secs: None,
+            help: None,
+        };
+
+        let result = run_shell(args, true);
+        let Err(err) = result else {
+            panic!("expected shell dry-run to reject --block-net + --upstream-proxy");
+        };
+        assert!(
+            err.to_string().contains("--block-net") && err.to_string().contains("--upstream-proxy"),
+            "unexpected error: {err}"
+        );
+    }
 
     #[test]
     fn wrap_rejects_caps_carrying_a_memory_limit() {
diff --git a/crates/nono-cli/src/launch_runtime.rs b/crates/nono-cli/src/launch_runtime.rs
index 40e50bc1a..e086e8701 100644
--- a/crates/nono-cli/src/launch_runtime.rs
+++ b/crates/nono-cli/src/launch_runtime.rs
@@ -3,7 +3,7 @@ use crate::config;
 use crate::proxy_runtime::prepare_proxy_launch_options;
 use crate::sandbox_prepare::{
     PreparedSandbox, prepare_sandbox, print_allow_gpu_warning, print_allow_launch_services_warning,
-    validate_block_net_conflicts,
+    validate_proxy_conflicts,
 };
 use crate::{exec_strategy, instruction_deny, profile, trust_scan};
 use colored::Colorize;
@@ -346,7 +346,7 @@ pub(crate) fn prepare_run_launch_plan(
     }
 
     let mut prepared = prepare_sandbox(&args, silent)?;
-    validate_block_net_conflicts(&args, &prepared)?;
+    validate_proxy_conflicts(&args, &prepared)?;
     validate_rollback_destination(run_args.rollback_dest.as_ref(), &prepared)?;
 
     if prepared.allow_launch_services_active {
@@ -641,3 +641,87 @@ pub(crate) fn select_threading_context(
         exec_strategy::ThreadingContext::Strict
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::cli::SandboxArgs;
+
+    fn run_args_with_sandbox(sandbox: SandboxArgs) -> RunArgs {
+        RunArgs {
+            sandbox,
+            detached: false,
+            detach_timeout_secs: None,
+            rollback: false,
+            no_rollback_prompt: false,
+            no_rollback: false,
+            rollback_exclude: Vec::new(),
+            rollback_include: Vec::new(),
+            rollback_all: false,
+            skip_dir: Vec::new(),
+            rollback_dest: None,
+            no_diagnostics: false,
+            diagnostics_json: false,
+            startup_timeout_secs: None,
+            no_audit: false,
+            no_audit_integrity: false,
+            audit_integrity: false,
+            audit_sign_key: None,
+            trust_override: false,
+            name: None,
+            capability_elevation: false,
+            command: Vec::new(),
+            help: None,
+        }
+    }
+
+    #[test]
+    fn run_launch_plan_rejects_block_net_with_upstream_proxy() {
+        let _env_lock = crate::test_env::ENV_LOCK.lock().expect("env lock");
+        let test_root = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+            .join("..")
+            .join("..")
+            .join("target")
+            .join("test-env")
+            .join(format!(
+                "run-launch-block-net-upstream-proxy-{}",
+                std::process::id()
+            ));
+        let home = test_root.join("home");
+        let state = test_root.join("state");
+        let config = test_root.join("config");
+        let workdir = test_root.join("workdir");
+        std::fs::create_dir_all(&home).expect("create test home");
+        std::fs::create_dir_all(&state).expect("create test state");
+        std::fs::create_dir_all(&config).expect("create test config");
+        std::fs::create_dir_all(&workdir).expect("create test workdir");
+        let _env = crate::test_env::EnvVarGuard::set_all(&[
+            ("HOME", home.to_str().expect("home path is utf-8")),
+            (
+                "XDG_STATE_HOME",
+                state.to_str().expect("state path is utf-8"),
+            ),
+            (
+                "XDG_CONFIG_HOME",
+                config.to_str().expect("config path is utf-8"),
+            ),
+        ]);
+
+        let run_args = run_args_with_sandbox(SandboxArgs {
+            allow_cwd: true,
+            workdir: Some(workdir),
+            block_net: true,
+            external_proxy: Some("squid.corp:3128".to_string()),
+            ..SandboxArgs::default()
+        });
+
+        let result = prepare_run_launch_plan(run_args, OsString::from("/bin/echo"), vec![], true);
+        let Err(err) = result else {
+            panic!("expected run launch plan to reject --block-net + --upstream-proxy");
+        };
+        assert!(
+            err.to_string().contains("--block-net") && err.to_string().contains("--upstream-proxy"),
+            "unexpected error: {err}"
+        );
+    }
+}
diff --git a/crates/nono-cli/src/proxy_runtime.rs b/crates/nono-cli/src/proxy_runtime.rs
index b296b344e..9aa16444a 100644
--- a/crates/nono-cli/src/proxy_runtime.rs
+++ b/crates/nono-cli/src/proxy_runtime.rs
@@ -1462,7 +1462,8 @@ pub(crate) fn prepare_proxy_launch_options(
     let has_credentials = !credentials.is_empty();
     let would_activate = has_domain_filter || has_credentials || upstream_proxy_addr.is_some();
 
-    // --block-net always wins; profile network.block yields to any proxy config.
+    // Normal launch validation rejects hard-block plus proxy-mode inputs before
+    // this fallback can choose BlockAll or strict filtering.
     let block_wins = args.block_net || (prepared.profile_network_block && !would_activate);
     if block_wins {
         if would_activate {
@@ -1480,7 +1481,6 @@ pub(crate) fn prepare_proxy_launch_options(
         return Ok(NetworkIntent::BlockAll);
     }
 
-    // Profile network.block + proxy flags → strict mode: deny unlisted hosts.
     let strict_filter = prepared.profile_network_block;
 
     let (plain_entries, endpoint_entries): (Vec<_>, Vec<_>) = allow_domain
diff --git a/crates/nono-cli/src/sandbox_prepare.rs b/crates/nono-cli/src/sandbox_prepare.rs
index 8521d6d36..161f9d4d2 100644
--- a/crates/nono-cli/src/sandbox_prepare.rs
+++ b/crates/nono-cli/src/sandbox_prepare.rs
@@ -771,14 +771,17 @@ fn has_proxy_intent(args: &SandboxArgs, prepared: &PreparedSandbox) -> bool {
         || prepared.upstream_proxy.is_some()
 }
 
+fn has_upstream_proxy(args: &SandboxArgs, prepared: &PreparedSandbox) -> bool {
+    args.external_proxy.is_some() || prepared.upstream_proxy.is_some()
+}
+
 pub(crate) fn validate_external_proxy_bypass(
     args: &SandboxArgs,
     prepared: &PreparedSandbox,
 ) -> Result<()> {
     let has_bypass = !args.external_proxy_bypass.is_empty() || !prepared.upstream_bypass.is_empty();
-    let has_external_proxy = args.external_proxy.is_some() || prepared.upstream_proxy.is_some();
 
-    if has_bypass && !has_external_proxy {
+    if has_bypass && !has_upstream_proxy(args, prepared) {
         return Err(NonoError::ConfigParse(
             "--upstream-bypass requires --upstream-proxy \
              (or upstream_proxy in profile network config)"
@@ -788,6 +791,14 @@ pub(crate) fn validate_external_proxy_bypass(
     Ok(())
 }
 
+pub(crate) fn validate_proxy_conflicts(
+    args: &SandboxArgs,
+    prepared: &PreparedSandbox,
+) -> Result<()> {
+    validate_block_net_conflicts(args, prepared)?;
+    validate_external_proxy_bypass(args, prepared)
+}
+
 /// Validate that `--block-net` is not combined with flags that imply proxy
 /// mode, and that `--allow-endpoint` always has a matching credential.
 ///
@@ -830,6 +841,14 @@ pub(crate) fn validate_block_net_conflicts(
                     .to_string(),
             ));
         }
+
+        if has_upstream_proxy(args, prepared) {
+            return Err(NonoError::ConfigParse(
+                "--block-net and --upstream-proxy are contradictory: \
+                 upstream proxy routing requires proxy mode"
+                    .to_string(),
+            ));
+        }
     }
 
     // --allow-endpoint without any credential is a no-op (and almost certainly
@@ -2486,6 +2505,24 @@ mod tests {
         );
     }
 
+    #[test]
+    fn block_net_with_upstream_proxy_errors() {
+        let args = SandboxArgs {
+            block_net: true,
+            external_proxy: Some("squid.corp:3128".to_string()),
+            ..Default::default()
+        };
+        let prepared = empty_prepared();
+        let result = validate_block_net_conflicts(&args, &prepared);
+        let Err(err) = result else {
+            panic!("expected error for --block-net + --upstream-proxy");
+        };
+        assert!(
+            err.to_string().contains("--block-net") && err.to_string().contains("--upstream-proxy"),
+            "unexpected error: {err}"
+        );
+    }
+
     #[test]
     fn block_net_alone_is_valid() {
         let args = SandboxArgs {
@@ -2510,6 +2547,22 @@ mod tests {
         );
     }
 
+    #[test]
+    fn profile_network_block_with_upstream_proxy_from_profile_errors() {
+        let args = SandboxArgs::default();
+        let mut prepared = empty_prepared();
+        prepared.profile_network_block = true;
+        prepared.upstream_proxy = Some("squid.corp:3128".to_string());
+        let result = validate_block_net_conflicts(&args, &prepared);
+        let Err(err) = result else {
+            panic!("expected error for profile network block + profile upstream proxy");
+        };
+        assert!(
+            err.to_string().contains("--block-net") && err.to_string().contains("--upstream-proxy"),
+            "unexpected error: {err}"
+        );
+    }
+
     #[test]
     fn allow_endpoint_without_credential_errors() {
         let args = SandboxArgs {