diff --git a/.github/workflows/dylint.yml b/.github/workflows/dylint.yml
index 6fbae0e8f..43ed82a50 100644
--- a/.github/workflows/dylint.yml
+++ b/.github/workflows/dylint.yml
@@ -183,9 +183,10 @@ jobs:
         env:
           FBUILD_PLATFORM_BOUNDARY_OBSERVED: ${{ github.workspace }}/target/platform-boundary-dylint-observed.tsv
         run: |
-          # Force fresh traversal so the independent observation ledger sees
-          # every platform-gated source path on each run.
-          export RUSTFLAGS="${RUSTFLAGS:+${RUSTFLAGS} }--cfg fbuild_platform_boundary_observation_run_${GITHUB_RUN_ID}"
+          # Force fresh workspace traversal for the observation ledger while
+          # preserving Cargo's cached dependencies. A per-run RUSTFLAGS value
+          # invalidated every dependency, causing a cold rebuild on each run.
+          rg --files crates -g '*.rs' -0 | xargs -0 -r touch
           rm -f "$FBUILD_PLATFORM_BOUNDARY_OBSERVED"
           env -u RUSTUP_TOOLCHAIN soldr dylint --all -- --workspace --all-targets
       - name: Compare scanner with actual Dylint observations
diff --git a/crates/fbuild-cli/tests/ci_command.rs b/crates/fbuild-cli/tests/ci_command.rs
index e7ac200ba..6f83e423f 100644
--- a/crates/fbuild-cli/tests/ci_command.rs
+++ b/crates/fbuild-cli/tests/ci_command.rs
@@ -44,7 +44,8 @@ fn run_cli_or_timeout(mut cmd: Command) -> Output {
 
 #[test]
 fn ci_help_lists_pio_compat_flags() {
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
     // allow-direct-spawn: integration test driver invoking the compiled fbuild binary.
     let mut cmd = Command::new(bin);
     cmd.args(["ci", "--help"]);
@@ -76,7 +77,8 @@ fn ci_help_lists_pio_compat_flags() {
 
 #[test]
 fn ci_without_board_is_a_usage_error() {
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
     // allow-direct-spawn: integration test driver.
     let mut cmd = Command::new(bin);
     cmd.args(["ci", "examples/Blink/Blink.ino"]);
@@ -92,7 +94,8 @@ fn ci_without_board_is_a_usage_error() {
 
 #[test]
 fn ci_without_sketches_is_a_usage_error() {
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
     // allow-direct-spawn: integration test driver.
     let mut cmd = Command::new(bin);
     cmd.args(["ci", "--board", "uno"]);
diff --git a/crates/fbuild-cli/tests/daemon_crash_recovery.rs b/crates/fbuild-cli/tests/daemon_crash_recovery.rs
index e0947db7c..24b183879 100644
--- a/crates/fbuild-cli/tests/daemon_crash_recovery.rs
+++ b/crates/fbuild-cli/tests/daemon_crash_recovery.rs
@@ -57,7 +57,8 @@ fn free_port() -> u16 {
 }
 
 fn cli_command(args: &[&str], port: u16, cache_dir: &std::path::Path) -> Command {
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
     // allow-direct-spawn: test driver invoking the fbuild CLI binary under test.
     let mut command = Command::new(bin);
     command
@@ -173,7 +174,9 @@ fn client_recovers_after_daemon_is_killed_uncleanly() {
     // The production spawn path resolves the daemon binary as a sibling of
     // the CLI. Under `cargo test --workspace` (and any full build) it exists;
     // under an isolated `-p fbuild-cli` test run it may not — skip then.
-    let cli = NormalizedPath::new(env!("CARGO_BIN_EXE_fbuild"));
+    let cli = NormalizedPath::new(
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild"),
+    );
     let daemon_name = fbuild_core::platform::executable::name("fbuild-daemon", "fbuild-daemon.exe");
     let sibling = cli
         .parent()
diff --git a/crates/fbuild-cli/tests/lib_select.rs b/crates/fbuild-cli/tests/lib_select.rs
index 87aebb375..d6c3de0a1 100644
--- a/crates/fbuild-cli/tests/lib_select.rs
+++ b/crates/fbuild-cli/tests/lib_select.rs
@@ -46,7 +46,8 @@ fn run_cli_or_timeout(mut cmd: Command) -> Output {
 /// `fbuild lib-select --help` must exit 0 and document both modes.
 #[test]
 fn lib_select_help_lists_command() {
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
     // allow-direct-spawn: integration test driver invoking the compiled fbuild binary.
     let mut cmd = Command::new(bin);
     cmd.args(["lib-select", "--help"]);
@@ -76,7 +77,8 @@ fn lib_select_help_lists_command() {
 /// the precise code, only that callers (CI, scripts) can detect the error.
 #[test]
 fn lib_select_missing_project_exits_nonzero() {
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
     // allow-direct-spawn: integration test driver invoking the compiled fbuild binary.
     let mut cmd = Command::new(bin);
     cmd.args([
@@ -101,7 +103,8 @@ fn lib_select_missing_project_exits_nonzero() {
 /// Passing both must fail at argument-parse time, not silently pick one.
 #[test]
 fn lib_select_explain_and_json_conflict() {
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
     // allow-direct-spawn: integration test driver invoking the compiled fbuild binary.
     let mut cmd = Command::new(bin);
     cmd.args(["lib-select", ".", "--explain", "--json"]);
diff --git a/crates/fbuild-cli/tests/test_emu_exit_code.rs b/crates/fbuild-cli/tests/test_emu_exit_code.rs
index 22795605a..a6b24572f 100644
--- a/crates/fbuild-cli/tests/test_emu_exit_code.rs
+++ b/crates/fbuild-cli/tests/test_emu_exit_code.rs
@@ -173,7 +173,8 @@ fn deploy_output_survives_nonzero_exit() {
     let port = spawn_mock_daemon(Arc::clone(&stop));
 
     let project = make_test_project();
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
 
     // allow-direct-spawn: integration test driver that invokes the compiled fbuild binary.
     let mut cmd = Command::new(bin);
@@ -215,7 +216,8 @@ fn test_emu_exits_non_zero_when_daemon_returns_failure() {
     let port = spawn_mock_daemon(Arc::clone(&stop));
 
     let project = make_test_project();
-    let bin = env!("CARGO_BIN_EXE_fbuild");
+    let bin =
+        option_env!("CARGO_BIN_EXE_fbuild").expect("cargo test must provide CARGO_BIN_EXE_fbuild");
 
     // Drive the CLI at the mock daemon. We clear FBUILD_DEV_MODE so the
     // CLI sticks to prod-mode path assumptions, and pin
diff --git a/crates/fbuild-daemon/tests/legacy_daemon_transition.rs b/crates/fbuild-daemon/tests/legacy_daemon_transition.rs
index 8c1d1bbd7..a65add778 100644
--- a/crates/fbuild-daemon/tests/legacy_daemon_transition.rs
+++ b/crates/fbuild-daemon/tests/legacy_daemon_transition.rs
@@ -192,7 +192,8 @@ async fn wait_for_http_health(port: u16, timeout: Duration) -> bool {
 async fn real_daemon_root_ownership_released_on_kill() {
     let temp_home = tempfile::tempdir().expect("temp home");
     let port = free_port();
-    let bin = env!("CARGO_BIN_EXE_fbuild-daemon");
+    let bin = option_env!("CARGO_BIN_EXE_fbuild-daemon")
+        .expect("cargo test must provide CARGO_BIN_EXE_fbuild-daemon");
     let home_key = if fbuild_core::platform::host::is_windows() {
         "USERPROFILE"
     } else {
diff --git a/crates/fbuild-daemon/tests/port_recovery.rs b/crates/fbuild-daemon/tests/port_recovery.rs
index dc36f5bfe..fbe9a54c3 100644
--- a/crates/fbuild-daemon/tests/port_recovery.rs
+++ b/crates/fbuild-daemon/tests/port_recovery.rs
@@ -58,7 +58,8 @@ fn wait_with_timeout(child: &mut Child, budget: Duration) -> bool {
 #[ignore = "expects a real fbuild-daemon binary; run with --ignored"]
 fn daemon_rebinds_cleanly_after_hard_kill_with_open_connection() {
     let port: u16 = 18900; // dedicated test port, avoids 8765 collisions
-    let bin = env!("CARGO_BIN_EXE_fbuild-daemon");
+    let bin = option_env!("CARGO_BIN_EXE_fbuild-daemon")
+        .expect("cargo test must provide CARGO_BIN_EXE_fbuild-daemon");
 
     // 1) Spawn the first daemon.
     // allow-direct-spawn: test driver spawns the real fbuild-daemon binary under test.
diff --git a/crates/fbuild-daemon/tests/process_containment.rs b/crates/fbuild-daemon/tests/process_containment.rs
index 220eacdff..3d383448f 100644
--- a/crates/fbuild-daemon/tests/process_containment.rs
+++ b/crates/fbuild-daemon/tests/process_containment.rs
@@ -60,7 +60,8 @@ fn wait_with_timeout(child: &mut Child, budget: Duration) -> bool {
 #[test]
 #[ignore = "spawns real subprocesses and issues hard-kills; run with --ignored"]
 fn daemon_children_die_when_daemon_dies() {
-    let harness = env!("CARGO_BIN_EXE_containment_harness");
+    let harness = option_env!("CARGO_BIN_EXE_containment_harness")
+        .expect("cargo test must provide CARGO_BIN_EXE_containment_harness");
 
     // Start the parent role.
     // allow-direct-spawn: integration-test driver invoking the containment harness binary.