diff --git a/crates/fbuild-build-arm/src/generic_arm/arm_linker.rs b/crates/fbuild-build-arm/src/generic_arm/arm_linker.rs
index 61e68eff9..3d2f9d5b6 100644
--- a/crates/fbuild-build-arm/src/generic_arm/arm_linker.rs
+++ b/crates/fbuild-build-arm/src/generic_arm/arm_linker.rs
@@ -227,6 +227,8 @@ impl Linker for ArmLinker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "arm-none-eabi-objcopy",
+            // Absolute toolchain path; no caller-PATH overlay needed (#1219).
+            None,
         )
         .await
     }
diff --git a/crates/fbuild-build-arm/src/nrf52/nrf52_linker.rs b/crates/fbuild-build-arm/src/nrf52/nrf52_linker.rs
index 42602ca5a..7b863ebfe 100644
--- a/crates/fbuild-build-arm/src/nrf52/nrf52_linker.rs
+++ b/crates/fbuild-build-arm/src/nrf52/nrf52_linker.rs
@@ -152,6 +152,8 @@ impl Linker for Nrf52Linker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "arm-none-eabi-objcopy",
+            // Absolute toolchain path; no caller-PATH overlay needed (#1219).
+            None,
         )
         .await
     }
diff --git a/crates/fbuild-build-arm/src/renesas/renesas_linker.rs b/crates/fbuild-build-arm/src/renesas/renesas_linker.rs
index e7b72f66f..e3e86e878 100644
--- a/crates/fbuild-build-arm/src/renesas/renesas_linker.rs
+++ b/crates/fbuild-build-arm/src/renesas/renesas_linker.rs
@@ -157,6 +157,8 @@ impl Linker for RenesasLinker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "arm-none-eabi-objcopy",
+            // Absolute toolchain path; no caller-PATH overlay needed (#1219).
+            None,
         )
         .await
     }
diff --git a/crates/fbuild-build-arm/src/sam/sam_linker.rs b/crates/fbuild-build-arm/src/sam/sam_linker.rs
index d9fb9b395..3344f11b7 100644
--- a/crates/fbuild-build-arm/src/sam/sam_linker.rs
+++ b/crates/fbuild-build-arm/src/sam/sam_linker.rs
@@ -173,6 +173,8 @@ impl Linker for SamLinker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "arm-none-eabi-objcopy",
+            // Absolute toolchain path; no caller-PATH overlay needed (#1219).
+            None,
         )
         .await
     }
diff --git a/crates/fbuild-build-arm/src/silabs/silabs_linker.rs b/crates/fbuild-build-arm/src/silabs/silabs_linker.rs
index d77fe6e91..bde730cb7 100644
--- a/crates/fbuild-build-arm/src/silabs/silabs_linker.rs
+++ b/crates/fbuild-build-arm/src/silabs/silabs_linker.rs
@@ -160,6 +160,8 @@ impl Linker for SilabsLinker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "arm-none-eabi-objcopy",
+            // Absolute toolchain path; no caller-PATH overlay needed (#1219).
+            None,
         )
         .await
     }
diff --git a/crates/fbuild-build-arm/src/teensy/teensy_linker.rs b/crates/fbuild-build-arm/src/teensy/teensy_linker.rs
index cb575c902..0bf5d4ff6 100644
--- a/crates/fbuild-build-arm/src/teensy/teensy_linker.rs
+++ b/crates/fbuild-build-arm/src/teensy/teensy_linker.rs
@@ -204,6 +204,8 @@ impl Linker for TeensyLinker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "arm-none-eabi-objcopy",
+            // Absolute toolchain path; no caller-PATH overlay needed (#1219).
+            None,
         )
         .await
     }
diff --git a/crates/fbuild-build-engine/src/build_fingerprint/mod.rs b/crates/fbuild-build-engine/src/build_fingerprint/mod.rs
index f18716a5a..c29e29be7 100644
--- a/crates/fbuild-build-engine/src/build_fingerprint/mod.rs
+++ b/crates/fbuild-build-engine/src/build_fingerprint/mod.rs
@@ -59,6 +59,14 @@ pub struct BinArtifactCache {
     pub flash_mode: String,
     pub flash_freq: String,
     pub flash_size: String,
+    /// Fingerprint of the esptool resolution that produced firmware.bin.
+    /// Empty when esptool is an absolute path (the resolution cannot
+    /// drift); a short hash of the caller's PATH when a bare-name spawn
+    /// resolves against it, so two requests with different caller PATHs
+    /// never share a cached bin (FastLED/fbuild#1219). `serde(default)`
+    /// keeps pre-existing absolute-path cache records valid.
+    #[serde(default)]
+    pub esptool_fingerprint: String,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
diff --git a/crates/fbuild-build-engine/src/lib.rs b/crates/fbuild-build-engine/src/lib.rs
index b1fdf440c..26ad83e21 100644
--- a/crates/fbuild-build-engine/src/lib.rs
+++ b/crates/fbuild-build-engine/src/lib.rs
@@ -177,6 +177,12 @@ pub struct BuildParams {
     /// actually emitted. This unblocks per-symbol bloat analysis on
     /// over-budget builds. See FastLED/fbuild#594.
     pub bloat_analysis: bool,
+    /// Snapshot of the calling CLI's PATH, forwarded per request so
+    /// bare-name tool spawns (esptool, python, objcopy) resolve against
+    /// the caller's PATH instead of the daemon's potentially stale one.
+    /// `None` when no request context exists (tests, local CLI paths).
+    /// See FastLED/fbuild#1219.
+    pub caller_path: Option<String>,
 }
 
 /// Trait for platform-specific build orchestrators.
diff --git a/crates/fbuild-build-engine/src/linker.rs b/crates/fbuild-build-engine/src/linker.rs
index b16dae119..7608c1f92 100644
--- a/crates/fbuild-build-engine/src/linker.rs
+++ b/crates/fbuild-build-engine/src/linker.rs
@@ -466,6 +466,7 @@ impl LinkerBase {
         output_format: &str,
         remove_sections: &[String],
         tool_label: &str,
+        caller_path: Option<&str>,
     ) -> Result<PathBuf> {
         use fbuild_core::subprocess::run_command;
 
@@ -490,11 +491,14 @@ impl LinkerBase {
         args.push(hex_path.to_string_lossy().to_string());
 
         let args_ref: Vec<&str> = args.iter().map(|s| s.as_str()).collect();
+        // A bare objcopy name resolves against the caller's PATH; absolute
+        // toolchain paths are unaffected (FastLED/fbuild#1219).
+        let env = fbuild_core::subprocess::bare_name_path_overlay(args_ref[0], caller_path);
         // FastLED/fbuild#809: objcopy ELF→HEX/BIN bounded at 1 min.
         let result = run_command(
             &args_ref,
             None,
-            None,
+            env.as_ref().map(|e| &e[..]),
             Some(std::time::Duration::from_secs(60)),
         )
         .await?;
diff --git a/crates/fbuild-build-engine/src/pipeline/context.rs b/crates/fbuild-build-engine/src/pipeline/context.rs
index 4d44e460f..ccc59d5b5 100644
--- a/crates/fbuild-build-engine/src/pipeline/context.rs
+++ b/crates/fbuild-build-engine/src/pipeline/context.rs
@@ -69,9 +69,13 @@ impl BuildContext {
         let pio_overrides = fbuild_config::PioEnvOverrides::from_map(params.pio_env.clone());
         let config =
             fbuild_config::PlatformIOConfig::from_path_with_overrides(&ini_path, pio_overrides)?;
-        let overlay =
-            crate::script_runtime::resolve_extra_script_overlay(project_dir, env_name, &config)
-                .await?;
+        let overlay = crate::script_runtime::resolve_extra_script_overlay(
+            project_dir,
+            env_name,
+            &config,
+            params.caller_path.as_deref(),
+        )
+        .await?;
         if let Some(p) = perf.as_mut() {
             p.record("config-parse", t0.elapsed());
         }
diff --git a/crates/fbuild-build-engine/src/script_runtime.rs b/crates/fbuild-build-engine/src/script_runtime.rs
index 427cbb59f..906b17b36 100644
--- a/crates/fbuild-build-engine/src/script_runtime.rs
+++ b/crates/fbuild-build-engine/src/script_runtime.rs
@@ -41,6 +41,7 @@ pub async fn resolve_extra_script_overlay(
     project_dir: &Path,
     env_name: &str,
     config: &fbuild_config::PlatformIOConfig,
+    caller_path: Option<&str>,
 ) -> fbuild_core::Result<BuildOverlay> {
     let extra_scripts = config.get_extra_scripts(env_name)?;
     if extra_scripts.is_empty() {
@@ -61,7 +62,7 @@ pub async fn resolve_extra_script_overlay(
             .to_string(),
     };
 
-    let python = find_python().await.ok_or_else(|| {
+    let python = find_python(caller_path).await.ok_or_else(|| {
         fbuild_core::FbuildError::BuildFailed(
             "extra_scripts detected but no Python interpreter was found; \
              install Python or use --platformio"
@@ -116,10 +117,13 @@ pub async fn resolve_extra_script_overlay(
     // — config-time evaluation, never legitimately long. Bound to 60s
     // so a buggy or hostile script cannot wedge the daemon's build
     // pipeline indefinitely.
+    // The interpreter was resolved against the caller's PATH when it is a
+    // bare name — spawn it against the same PATH (FastLED/fbuild#1219).
+    let env = fbuild_core::subprocess::bare_name_path_overlay(argv[0], caller_path);
     let output = fbuild_core::subprocess::run_command(
         &argv,
         Some(project_dir),
-        None,
+        env.as_ref().map(|e| &e[..]),
         Some(std::time::Duration::from_secs(60)),
     )
     .await
@@ -298,7 +302,7 @@ fn libs_to_flags(
     Ok(flags)
 }
 
-pub async fn find_python() -> Option<Vec<String>> {
+pub async fn find_python(caller_path: Option<&str>) -> Option<Vec<String>> {
     let candidates: &[&[&str]] = if cfg!(windows) {
         &[&["python"], &["py", "-3"]]
     } else {
@@ -308,12 +312,15 @@ pub async fn find_python() -> Option<Vec<String>> {
     for candidate in candidates {
         let mut argv: Vec<&str> = candidate.to_vec();
         argv.push("--version");
+        // Probe against the caller's PATH so the daemon finds the same
+        // interpreter the CLI's environment would (FastLED/fbuild#1219).
+        let env = fbuild_core::subprocess::bare_name_path_overlay(candidate[0], caller_path);
         // FastLED/fbuild#809: `python --version` on the startup path —
         // bound tightly so a hung interpreter cannot wedge build init.
         if let Ok(output) = fbuild_core::subprocess::run_command(
             &argv,
             None,
-            None,
+            env.as_ref().map(|e| &e[..]),
             Some(std::time::Duration::from_secs(5)),
         )
         .await
diff --git a/crates/fbuild-build-engine/src/script_runtime_tests.rs b/crates/fbuild-build-engine/src/script_runtime_tests.rs
index 618b088b7..3595c2f91 100644
--- a/crates/fbuild-build-engine/src/script_runtime_tests.rs
+++ b/crates/fbuild-build-engine/src/script_runtime_tests.rs
@@ -30,7 +30,7 @@ extra_scripts = {}
 async fn resolve_runtime_error(project_dir: &Path) -> String {
     let config =
         fbuild_config::PlatformIOConfig::from_path(&project_dir.join("platformio.ini")).unwrap();
-    resolve_extra_script_overlay(project_dir, "demo", &config)
+    resolve_extra_script_overlay(project_dir, "demo", &config, None)
         .await
         .unwrap_err()
         .to_string()
@@ -126,7 +126,7 @@ fn test_scope_to_link_overlay_maps_libpath_and_libs() {
 
 #[tokio::test]
 async fn test_resolve_extra_script_overlay_supports_dump_shim() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -159,7 +159,7 @@ env.Append(CPPDEFINES=[\"DUMP_SHIM_OK\"])
     let config =
         fbuild_config::PlatformIOConfig::from_path(&project_dir.join("platformio.ini")).unwrap();
     // Pinned to MockEnv (see resolve_runtime_overlay note).
-    let overlay = resolve_extra_script_overlay(project_dir, "demo", &config)
+    let overlay = resolve_extra_script_overlay(project_dir, "demo", &config, None)
         .await
         .unwrap();
     assert!(
@@ -172,7 +172,7 @@ env.Append(CPPDEFINES=[\"DUMP_SHIM_OK\"])
 
 #[tokio::test]
 async fn test_resolve_extra_script_overlay_supports_common_noop_scons_helpers() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -209,7 +209,7 @@ env.Append(CPPDEFINES=[\"HELPERS_SHIM_OK\"])
     let config =
         fbuild_config::PlatformIOConfig::from_path(&project_dir.join("platformio.ini")).unwrap();
     // Pinned to MockEnv (see resolve_runtime_overlay note).
-    let overlay = resolve_extra_script_overlay(project_dir, "demo", &config)
+    let overlay = resolve_extra_script_overlay(project_dir, "demo", &config, None)
         .await
         .unwrap();
     assert!(
@@ -222,7 +222,7 @@ env.Append(CPPDEFINES=[\"HELPERS_SHIM_OK\"])
 
 #[tokio::test]
 async fn test_resolve_extra_script_overlay_supports_board_config_shim() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -256,7 +256,7 @@ env.Append(CPPDEFINES=[\"BOARD_CONFIG_SHIM_OK\"])
     let config =
         fbuild_config::PlatformIOConfig::from_path(&project_dir.join("platformio.ini")).unwrap();
     // Pinned to MockEnv (see resolve_runtime_overlay note).
-    let overlay = resolve_extra_script_overlay(project_dir, "demo", &config)
+    let overlay = resolve_extra_script_overlay(project_dir, "demo", &config, None)
         .await
         .unwrap();
     assert!(
@@ -269,7 +269,7 @@ env.Append(CPPDEFINES=[\"BOARD_CONFIG_SHIM_OK\"])
 
 #[tokio::test]
 async fn test_resolve_extra_script_overlay_supports_pio_platform_shim() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -306,7 +306,7 @@ env.Append(CPPDEFINES=[\"PIO_PLATFORM_SHIM_OK\"])
     let config =
         fbuild_config::PlatformIOConfig::from_path(&project_dir.join("platformio.ini")).unwrap();
     // Pinned to MockEnv (see resolve_runtime_overlay note).
-    let overlay = resolve_extra_script_overlay(project_dir, "demo", &config)
+    let overlay = resolve_extra_script_overlay(project_dir, "demo", &config, None)
         .await
         .unwrap();
     assert!(
@@ -319,7 +319,7 @@ env.Append(CPPDEFINES=[\"PIO_PLATFORM_SHIM_OK\"])
 
 #[tokio::test]
 async fn test_resolve_extra_script_overlay_rejects_unsupported_script_prefix() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -344,7 +344,7 @@ Import(\"env\")
 /// corrupt the harness's JSON-on-stdout protocol.
 #[tokio::test]
 async fn test_resolve_extra_script_overlay_tolerates_user_stdout_noise() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -363,7 +363,7 @@ print(\"post-append noise\")
     );
     let config =
         fbuild_config::PlatformIOConfig::from_path(&temp.path().join("platformio.ini")).unwrap();
-    let overlay = resolve_extra_script_overlay(temp.path(), "demo", &config)
+    let overlay = resolve_extra_script_overlay(temp.path(), "demo", &config, None)
         .await
         .unwrap();
     assert!(
@@ -416,7 +416,7 @@ framework = arduino
 async fn resolve_runtime_overlay(project_dir: &Path) -> BuildOverlay {
     let config =
         fbuild_config::PlatformIOConfig::from_path(&project_dir.join("platformio.ini")).unwrap();
-    resolve_extra_script_overlay(project_dir, "demo", &config)
+    resolve_extra_script_overlay(project_dir, "demo", &config, None)
         .await
         .unwrap()
 }
@@ -428,7 +428,7 @@ async fn resolve_runtime_overlay(project_dir: &Path) -> BuildOverlay {
 /// `AddPostAction`. Source: MarlinFirmware/Marlin buildroot scripts.
 #[tokio::test]
 async fn test_shim_simple_marlin_cxxflags_style() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -477,7 +477,7 @@ env.AddPostAction(\"$PROGPATH\", lambda *a, **k: None)
 /// emit `-Dkey=value`, not a malformed array entry.
 #[tokio::test]
 async fn test_shim_simple_inplace_tuple_cppdefine() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -516,7 +516,7 @@ env.Append(CPPDEFINES=[\"PLAIN\"])
 /// `LINKFLAGS`, and registers a no-op post action.
 #[tokio::test]
 async fn test_shim_medium_default_environment_linkflags() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
@@ -554,7 +554,7 @@ env.AddPostAction(\"$BUILD_DIR/firmware.bin\", after_build)
 /// script must not hard-fail and the parallel flag mutation must land.
 #[tokio::test]
 async fn test_shim_medium_nonflag_scope_does_not_reject() {
-    if find_python().await.is_none() {
+    if find_python(None).await.is_none() {
         return;
     }
 
diff --git a/crates/fbuild-build-esp/src/esp32/esp32_linker.rs b/crates/fbuild-build-esp/src/esp32/esp32_linker.rs
index 374fafca0..86f151695 100644
--- a/crates/fbuild-build-esp/src/esp32/esp32_linker.rs
+++ b/crates/fbuild-build-esp/src/esp32/esp32_linker.rs
@@ -151,6 +151,9 @@ pub struct Esp32Linker {
     /// falls back to an `esptool` on PATH. See FastLED/fbuild#954.
     esptool_bin: Option<PathBuf>,
     verbose: bool,
+    /// Caller CLI's PATH snapshot for bare-name esptool resolution
+    /// (FastLED/fbuild#1219).
+    caller_path: Option<String>,
 }
 
 impl Esp32Linker {
@@ -171,6 +174,7 @@ impl Esp32Linker {
         max_ram: Option<u64>,
         esptool_bin: Option<PathBuf>,
         verbose: bool,
+        caller_path: Option<String>,
     ) -> Self {
         let flash_mode = flash_mode.unwrap_or_else(|| mcu_config.default_flash_mode().to_string());
         Self {
@@ -189,6 +193,7 @@ impl Esp32Linker {
             max_ram,
             esptool_bin,
             verbose,
+            caller_path,
         }
     }
 
@@ -239,6 +244,26 @@ impl Esp32Linker {
         output_dir.join(".firmware_size_cache.json")
     }
 
+    /// Fingerprint the esptool resolution feeding the BIN cache. A
+    /// provisioned absolute path cannot drift → empty (matches serde's
+    /// default for pre-existing cache records). A bare `esptool` resolved
+    /// against a caller PATH gets a short hash of that PATH so requests
+    /// with different caller PATHs never share a cached firmware.bin
+    /// (FastLED/fbuild#1219).
+    fn esptool_fingerprint(&self) -> String {
+        if self.esptool_bin.is_some() {
+            return String::new();
+        }
+        match self.caller_path.as_deref() {
+            Some(path) if !path.is_empty() => {
+                use sha2::{Digest, Sha256};
+                let digest = Sha256::digest(path.as_bytes());
+                digest[..8].iter().map(|b| format!("{b:02x}")).collect()
+            }
+            _ => String::new(),
+        }
+    }
+
     fn current_bin_cache(&self, elf_path: &Path, flash_size: &str) -> Result<BinArtifactCache> {
         Ok(BinArtifactCache {
             version: BUILD_FINGERPRINT_VERSION,
@@ -246,6 +271,7 @@ impl Esp32Linker {
             flash_mode: self.flash_mode.clone(),
             flash_freq: self.flash_freq.clone(),
             flash_size: flash_size.to_string(),
+            esptool_fingerprint: self.esptool_fingerprint(),
         })
     }
 
@@ -472,7 +498,18 @@ impl Linker for Esp32Linker {
 
         tracing::info!("elf2image: {}", argv.join(" "));
 
-        match run_command(&args, None, None, Some(std::time::Duration::from_secs(60))).await {
+        // Resolve a bare `esptool` fallback against the caller's PATH; the
+        // overlay no-ops when a provisioned absolute path is in use (#1219).
+        let env =
+            fbuild_core::subprocess::bare_name_path_overlay(args[0], self.caller_path.as_deref());
+        match run_command(
+            &args,
+            None,
+            env.as_ref().map(|e| &e[..]),
+            Some(std::time::Duration::from_secs(60)),
+        )
+        .await
+        {
             Ok(result) if result.success() => {
                 let cache = self.current_bin_cache(&elf_out, &flash_size)?;
                 if let Err(e) = save_json(&self.bin_cache_path(output_dir), &cache) {
@@ -562,9 +599,17 @@ mod tests {
             Some(327680),
             None,
             false,
+            None,
         )
     }
 
+    fn test_linker_with(esptool_bin: Option<PathBuf>, caller_path: Option<String>) -> Esp32Linker {
+        let mut linker = test_linker("esp32c6");
+        linker.esptool_bin = esptool_bin;
+        linker.caller_path = caller_path;
+        linker
+    }
+
     #[test]
     fn test_esp32_linker_creation() {
         let linker = test_linker("esp32c6");
@@ -572,6 +617,69 @@ mod tests {
         assert_eq!(linker.max_ram, Some(327680));
     }
 
+    /// FastLED/fbuild#1219 follow-up: with a bare-name esptool, two
+    /// requests with different caller PATHs may resolve different esptool
+    /// binaries — they must never share a cached firmware.bin.
+    #[test]
+    fn bare_name_esptool_bin_reuse_is_keyed_by_caller_path() {
+        let tmp = tempfile::TempDir::new().unwrap();
+        let elf = tmp.path().join("firmware.elf");
+        std::fs::write(&elf, b"elf").unwrap();
+
+        let linker_a = test_linker_with(None, Some("C:\\venv-a\\Scripts".to_string()));
+        let flash_size = linker_a.flash_size();
+
+        // Simulate a successful conversion by linker A.
+        std::fs::write(tmp.path().join("firmware.bin"), b"bin").unwrap();
+        let cache = linker_a.current_bin_cache(&elf, &flash_size).unwrap();
+        save_json(&linker_a.bin_cache_path(tmp.path()), &cache).unwrap();
+
+        assert!(
+            linker_a.can_reuse_bin(&elf, tmp.path(), &flash_size),
+            "same caller PATH must reuse the cached bin"
+        );
+
+        let linker_b = test_linker_with(None, Some("C:\\venv-b\\Scripts".to_string()));
+        assert!(
+            !linker_b.can_reuse_bin(&elf, tmp.path(), &flash_size),
+            "a different caller PATH must not reuse a bin produced by another PATH's esptool"
+        );
+
+        let linker_none = test_linker_with(None, None);
+        assert!(
+            !linker_none.can_reuse_bin(&elf, tmp.path(), &flash_size),
+            "no caller PATH (daemon-ambient resolution) must not reuse a caller-PATH bin"
+        );
+    }
+
+    /// Provisioned absolute-path esptool cannot drift with the caller's
+    /// PATH — caching must behave exactly as before #1219, including
+    /// across requests with different caller PATHs.
+    #[test]
+    fn absolute_esptool_bin_reuse_ignores_caller_path() {
+        let tmp = tempfile::TempDir::new().unwrap();
+        let elf = tmp.path().join("firmware.elf");
+        std::fs::write(&elf, b"elf").unwrap();
+
+        let esptool = PathBuf::from("C:\\tools\\esptool.exe");
+        let linker_a = test_linker_with(Some(esptool.clone()), Some("C:\\venv-a".to_string()));
+        let flash_size = linker_a.flash_size();
+
+        std::fs::write(tmp.path().join("firmware.bin"), b"bin").unwrap();
+        let cache = linker_a.current_bin_cache(&elf, &flash_size).unwrap();
+        assert!(
+            cache.esptool_fingerprint.is_empty(),
+            "absolute esptool must record the serde-default (empty) fingerprint"
+        );
+        save_json(&linker_a.bin_cache_path(tmp.path()), &cache).unwrap();
+
+        let linker_b = test_linker_with(Some(esptool), Some("C:\\venv-b".to_string()));
+        assert!(
+            linker_b.can_reuse_bin(&elf, tmp.path(), &flash_size),
+            "absolute-path esptool must keep reusing regardless of caller PATH"
+        );
+    }
+
     #[test]
     fn test_flash_size_uses_board_max_flash_for_elf2image_and_cache() {
         let config = get_mcu_config("esp32c6").unwrap();
@@ -592,6 +700,7 @@ mod tests {
             Some(327680),
             None,
             false,
+            None,
         );
         let tmp = tempfile::TempDir::new().unwrap();
         let elf = tmp.path().join("firmware.elf");
@@ -658,6 +767,7 @@ mod tests {
             Some(327680),
             None,
             false,
+            None,
         );
         let flags = linker.linker_flags();
         assert!(flags.iter().any(|f| f.contains("IDF_TARGET_ESP32C6")));
@@ -702,6 +812,7 @@ mod tests {
             Some(327680),
             None,
             false,
+            None,
         );
         let flags = linker.linker_flags();
         assert!(flags.contains(&"-mlongcalls".to_string()));
diff --git a/crates/fbuild-build-esp/src/esp32/orchestrator/boot_artifacts.rs b/crates/fbuild-build-esp/src/esp32/orchestrator/boot_artifacts.rs
index 83876d61c..70deeddbb 100644
--- a/crates/fbuild-build-esp/src/esp32/orchestrator/boot_artifacts.rs
+++ b/crates/fbuild-build-esp/src/esp32/orchestrator/boot_artifacts.rs
@@ -23,6 +23,7 @@ pub(super) async fn prepare_boot_artifacts(
     mcu_config: &Esp32McuConfig,
     flash_freq: &str,
     esptool_bin: Option<&Path>,
+    caller_path: Option<&str>,
     perf: &mut crate::perf_log::PerfTimer,
 ) -> Result<()> {
     let boot_artifacts_started = Instant::now();
@@ -91,10 +92,13 @@ pub(super) async fn prepare_boot_artifacts(
                 &boot_dst_str,
             );
             let args: Vec<&str> = argv.iter().map(|s| s.as_str()).collect();
+            // A bare `esptool` fallback resolves against the caller's PATH;
+            // provisioned absolute paths are unaffected (#1219).
+            let env = fbuild_core::subprocess::bare_name_path_overlay(args[0], caller_path);
             match fbuild_core::subprocess::run_command(
                 &args,
                 None,
-                None,
+                env.as_ref().map(|e| &e[..]),
                 Some(std::time::Duration::from_secs(60)),
             )
             .await
@@ -144,7 +148,7 @@ pub(super) async fn prepare_boot_artifacts(
             // `python` doesn't exist on modern distros (ubuntu 24.04 ships
             // only `python3`); resolve the interpreter the same way the
             // extra_scripts runtime does.
-            let python = crate::script_runtime::find_python()
+            let python = crate::script_runtime::find_python(caller_path)
                 .await
                 .unwrap_or_else(|| vec!["python".to_string()]);
             let mut args: Vec<&str> = python.iter().map(|s| s.as_str()).collect();
@@ -154,10 +158,12 @@ pub(super) async fn prepare_boot_artifacts(
                 parts_csv_str.as_ref(),
                 parts_dst_str.as_ref(),
             ]);
+            // Bare `python` spawn — resolve against the caller's PATH (#1219).
+            let env = fbuild_core::subprocess::bare_name_path_overlay(args[0], caller_path);
             match fbuild_core::subprocess::run_command(
                 &args,
                 None,
-                None,
+                env.as_ref().map(|e| &e[..]),
                 Some(std::time::Duration::from_secs(10)),
             )
             .await
diff --git a/crates/fbuild-build-esp/src/esp32/orchestrator/build.rs b/crates/fbuild-build-esp/src/esp32/orchestrator/build.rs
index 10f6a3425..25cb9d761 100644
--- a/crates/fbuild-build-esp/src/esp32/orchestrator/build.rs
+++ b/crates/fbuild-build-esp/src/esp32/orchestrator/build.rs
@@ -814,6 +814,7 @@ impl BuildOrchestrator for Esp32Orchestrator {
             ctx.board.max_ram,
             esptool_bin.clone().map(|path| path.into_path_buf()),
             params.verbose,
+            params.caller_path.clone(),
         );
 
         let link_result = {
@@ -842,6 +843,7 @@ impl BuildOrchestrator for Esp32Orchestrator {
             &mcu_config,
             &flash_freq,
             esptool_bin.as_ref().map(|path| path.as_path()),
+            params.caller_path.as_deref(),
             &mut perf,
         )
         .await?;
diff --git a/crates/fbuild-build-esp/src/esp8266/esp8266_linker.rs b/crates/fbuild-build-esp/src/esp8266/esp8266_linker.rs
index c2a57bd09..49f405576 100644
--- a/crates/fbuild-build-esp/src/esp8266/esp8266_linker.rs
+++ b/crates/fbuild-build-esp/src/esp8266/esp8266_linker.rs
@@ -37,6 +37,9 @@ pub struct Esp8266Linker {
     max_flash: Option<u64>,
     max_ram: Option<u64>,
     verbose: bool,
+    /// Caller CLI's PATH snapshot for bare-name esptool resolution
+    /// (FastLED/fbuild#1219).
+    caller_path: Option<String>,
 }
 
 impl Esp8266Linker {
@@ -57,6 +60,7 @@ impl Esp8266Linker {
         max_flash: Option<u64>,
         max_ram: Option<u64>,
         verbose: bool,
+        caller_path: Option<String>,
     ) -> Self {
         let flash_mode =
             flash_mode.unwrap_or_else(|| mcu_config.esptool.default_flash_mode.clone());
@@ -76,6 +80,7 @@ impl Esp8266Linker {
             max_flash,
             max_ram,
             verbose,
+            caller_path,
         }
     }
 }
@@ -275,7 +280,17 @@ impl Linker for Esp8266Linker {
             &bin_str,
         ];
 
-        match run_command(&args, None, None, Some(std::time::Duration::from_secs(30))).await {
+        // Bare `esptool` spawn — resolve it against the caller's PATH (#1219).
+        let env =
+            fbuild_core::subprocess::bare_name_path_overlay(args[0], self.caller_path.as_deref());
+        match run_command(
+            &args,
+            None,
+            env.as_ref().map(|e| &e[..]),
+            Some(std::time::Duration::from_secs(30)),
+        )
+        .await
+        {
             Ok(result) if result.success() => {
                 // Verify the output file was actually created with content.
                 // ESP8266 esptool may create segmented files (firmware.bin-0x00000.bin)
@@ -306,6 +321,7 @@ impl Linker for Esp8266Linker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "xtensa-lx106-elf-objcopy",
+            self.caller_path.as_deref(),
         )
         .await
     }
@@ -361,6 +377,7 @@ mod tests {
             Some(4_194_304),
             Some(81_920),
             false,
+            None,
         );
         assert!(
             linker
diff --git a/crates/fbuild-build-esp/src/esp8266/orchestrator.rs b/crates/fbuild-build-esp/src/esp8266/orchestrator.rs
index 686dbcaf3..b6a96783e 100644
--- a/crates/fbuild-build-esp/src/esp8266/orchestrator.rs
+++ b/crates/fbuild-build-esp/src/esp8266/orchestrator.rs
@@ -197,6 +197,7 @@ impl BuildOrchestrator for Esp8266Orchestrator {
             ctx.board.max_flash,
             ctx.board.max_ram,
             params.verbose,
+            params.caller_path.clone(),
         );
 
         // 8. Build LibraryBuildEnv for project-as-library compilation
diff --git a/crates/fbuild-build-mcu/src/avr/avr_linker.rs b/crates/fbuild-build-mcu/src/avr/avr_linker.rs
index 89065867b..d4bc73e60 100644
--- a/crates/fbuild-build-mcu/src/avr/avr_linker.rs
+++ b/crates/fbuild-build-mcu/src/avr/avr_linker.rs
@@ -213,6 +213,8 @@ impl Linker for AvrLinker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "avr-objcopy",
+            // Absolute toolchain path; no caller-PATH overlay needed (#1219).
+            None,
         )
         .await
     }
diff --git a/crates/fbuild-build-mcu/src/ch32v/ch32v_linker.rs b/crates/fbuild-build-mcu/src/ch32v/ch32v_linker.rs
index f193cdf94..b80638685 100644
--- a/crates/fbuild-build-mcu/src/ch32v/ch32v_linker.rs
+++ b/crates/fbuild-build-mcu/src/ch32v/ch32v_linker.rs
@@ -24,6 +24,9 @@ pub struct Ch32vLinker {
     max_ram: Option<u64>,
     memory_defsyms: Vec<String>,
     verbose: bool,
+    /// Caller CLI's PATH snapshot for bare-name objcopy resolution
+    /// (FastLED/fbuild#1219).
+    caller_path: Option<String>,
 }
 
 impl Ch32vLinker {
@@ -39,6 +42,7 @@ impl Ch32vLinker {
         max_flash: Option<u64>,
         max_ram: Option<u64>,
         verbose: bool,
+        caller_path: Option<String>,
     ) -> Self {
         Self {
             gcc_path,
@@ -52,6 +56,7 @@ impl Ch32vLinker {
             max_ram,
             memory_defsyms: Vec::new(),
             verbose,
+            caller_path,
         }
     }
 
@@ -153,6 +158,7 @@ impl Linker for Ch32vLinker {
             &self.mcu_config.objcopy.output_format,
             &self.mcu_config.objcopy.remove_sections,
             "riscv-none-elf-objcopy",
+            self.caller_path.as_deref(),
         )
         .await
     }
@@ -203,6 +209,7 @@ mod tests {
             Some(16384),
             Some(2048),
             false,
+            None,
         );
         assert_eq!(linker.max_flash, Some(16384));
         assert_eq!(linker.max_ram, Some(2048));
@@ -221,6 +228,7 @@ mod tests {
             Some(16384),
             Some(2048),
             false,
+            None,
         );
         assert!(
             linker
@@ -243,6 +251,7 @@ mod tests {
             None,
             None,
             false,
+            None,
         )
         .with_memory_defsyms(vec![
             "-Wl,--defsym=__FLASH_SIZE=32768".into(),
@@ -278,6 +287,7 @@ mod tests {
             None,
             None,
             false,
+            None,
         );
         let args = linker.build_link_args(
             &[],
diff --git a/crates/fbuild-build-mcu/src/ch32v/orchestrator.rs b/crates/fbuild-build-mcu/src/ch32v/orchestrator.rs
index 871a5cfba..82d6cf960 100644
--- a/crates/fbuild-build-mcu/src/ch32v/orchestrator.rs
+++ b/crates/fbuild-build-mcu/src/ch32v/orchestrator.rs
@@ -210,6 +210,7 @@ impl BuildOrchestrator for Ch32vOrchestrator {
             ctx.board.max_flash,
             ctx.board.max_ram,
             params.verbose,
+            params.caller_path.clone(),
         )
         .with_memory_defsyms(memory_defsyms);
 
diff --git a/crates/fbuild-build/src/compile_many.rs b/crates/fbuild-build/src/compile_many.rs
index c29e49e0f..2bfe39d7d 100644
--- a/crates/fbuild-build/src/compile_many.rs
+++ b/crates/fbuild-build/src/compile_many.rs
@@ -373,6 +373,7 @@ async fn build_one_sketch(inputs: SketchBuildInputs) -> SketchResult {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let outcome = match get_orchestrator(platform) {
diff --git a/crates/fbuild-build/tests/avr_build.rs b/crates/fbuild-build/tests/avr_build.rs
index 2a016de2b..6d25bc27c 100644
--- a/crates/fbuild-build/tests/avr_build.rs
+++ b/crates/fbuild-build/tests/avr_build.rs
@@ -128,6 +128,7 @@ async fn build_uno_minimal() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::avr::orchestrator::AvrOrchestrator;
@@ -226,6 +227,7 @@ async fn compare_with_python_output() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::avr::orchestrator::AvrOrchestrator;
@@ -318,6 +320,7 @@ void loop() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::avr::orchestrator::AvrOrchestrator;
@@ -385,6 +388,7 @@ fn uno_build_params(project_dir: &Path, build_dir: PathBuf, clean: bool) -> Buil
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     }
 }
 
diff --git a/crates/fbuild-build/tests/clangd_check_parity.rs b/crates/fbuild-build/tests/clangd_check_parity.rs
index 00181b3d6..d684e5642 100644
--- a/crates/fbuild-build/tests/clangd_check_parity.rs
+++ b/crates/fbuild-build/tests/clangd_check_parity.rs
@@ -160,6 +160,7 @@ async fn clangd_check_parity_uno() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = AvrOrchestrator;
diff --git a/crates/fbuild-build/tests/eh_frame_strip_esp32.rs b/crates/fbuild-build/tests/eh_frame_strip_esp32.rs
index 80804e329..0078f9ad1 100644
--- a/crates/fbuild-build/tests/eh_frame_strip_esp32.rs
+++ b/crates/fbuild-build/tests/eh_frame_strip_esp32.rs
@@ -54,6 +54,7 @@ fn make_params(project_dir: &Path) -> BuildParams {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     }
 }
 
diff --git a/crates/fbuild-build/tests/esp32_build.rs b/crates/fbuild-build/tests/esp32_build.rs
index 6afc16bdf..d070edafa 100644
--- a/crates/fbuild-build/tests/esp32_build.rs
+++ b/crates/fbuild-build/tests/esp32_build.rs
@@ -98,6 +98,7 @@ void loop() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
@@ -190,6 +191,7 @@ void loop() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
@@ -275,6 +277,7 @@ void loop() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
@@ -361,6 +364,7 @@ void loop() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
@@ -437,6 +441,7 @@ async fn build_esp32s3_fixture() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
@@ -505,6 +510,7 @@ async fn build_nightdriverstrip_demo() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
@@ -604,6 +610,7 @@ async fn incremental_build_at(project_dir: &std::path::Path, env_name: &str) {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
@@ -703,6 +710,7 @@ async fn incremental_nightdriverstrip_one_file_changed() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
diff --git a/crates/fbuild-build/tests/lite_scons_acceptance.rs b/crates/fbuild-build/tests/lite_scons_acceptance.rs
index f2e4801ee..036cfddf8 100644
--- a/crates/fbuild-build/tests/lite_scons_acceptance.rs
+++ b/crates/fbuild-build/tests/lite_scons_acceptance.rs
@@ -95,7 +95,7 @@ fn write_project(extra_scripts: &str, scripts: &[(&str, &str)]) -> tempfile::Tem
 async fn resolve_lite(project_dir: &Path) -> BuildOverlay {
     let config = fbuild_config::PlatformIOConfig::from_path(&project_dir.join("platformio.ini"))
         .expect("parse platformio.ini");
-    resolve_extra_script_overlay(project_dir, "demo", &config)
+    resolve_extra_script_overlay(project_dir, "demo", &config, None)
         .await
         .expect("lite-SCons harness must succeed for the 5 spike patterns")
 }
diff --git a/crates/fbuild-build/tests/nxplpc_build_flags.rs b/crates/fbuild-build/tests/nxplpc_build_flags.rs
index 57484ab55..29076d3c8 100644
--- a/crates/fbuild-build/tests/nxplpc_build_flags.rs
+++ b/crates/fbuild-build/tests/nxplpc_build_flags.rs
@@ -85,6 +85,7 @@ async fn lpc845brk_propagates_build_flags_to_library_compile_587() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::nxplpc::orchestrator::NxpLpcOrchestrator;
diff --git a/crates/fbuild-build/tests/nxplpc_core_compile_commands.rs b/crates/fbuild-build/tests/nxplpc_core_compile_commands.rs
index 77769c092..a10e20784 100644
--- a/crates/fbuild-build/tests/nxplpc_core_compile_commands.rs
+++ b/crates/fbuild-build/tests/nxplpc_core_compile_commands.rs
@@ -56,6 +56,7 @@ async fn build_core_repo(repo: &Path, env_name: &str) -> tempfile::TempDir {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::nxplpc::orchestrator::NxpLpcOrchestrator;
diff --git a/crates/fbuild-build/tests/stm32_acceptance.rs b/crates/fbuild-build/tests/stm32_acceptance.rs
index 784f4821f..c6cd0c1b3 100644
--- a/crates/fbuild-build/tests/stm32_acceptance.rs
+++ b/crates/fbuild-build/tests/stm32_acceptance.rs
@@ -104,6 +104,7 @@ async fn stm32f103c8_blink_with_spi_auto_discovers_library_205_ac4() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::stm32::orchestrator::Stm32Orchestrator;
diff --git a/crates/fbuild-build/tests/teensy30_acceptance.rs b/crates/fbuild-build/tests/teensy30_acceptance.rs
index 63229ed20..0391cf9d0 100644
--- a/crates/fbuild-build/tests/teensy30_acceptance.rs
+++ b/crates/fbuild-build/tests/teensy30_acceptance.rs
@@ -122,6 +122,7 @@ async fn teensy30_analog_output_meets_205_ac2() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let result =
diff --git a/crates/fbuild-build/tests/teensy_build.rs b/crates/fbuild-build/tests/teensy_build.rs
index 8ada8f25c..de7304df5 100644
--- a/crates/fbuild-build/tests/teensy_build.rs
+++ b/crates/fbuild-build/tests/teensy_build.rs
@@ -96,6 +96,7 @@ void loop() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::teensy::orchestrator::TeensyOrchestrator;
@@ -171,6 +172,7 @@ void loop() {}
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::teensy::orchestrator::TeensyOrchestrator;
@@ -224,6 +226,7 @@ async fn build_teensy41_fixture() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::teensy::orchestrator::TeensyOrchestrator;
@@ -336,6 +339,7 @@ void loop() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::teensy::orchestrator::TeensyOrchestrator;
diff --git a/crates/fbuild-build/tests/teensylc_acceptance.rs b/crates/fbuild-build/tests/teensylc_acceptance.rs
index 44c215533..72a6d7a38 100644
--- a/crates/fbuild-build/tests/teensylc_acceptance.rs
+++ b/crates/fbuild-build/tests/teensylc_acceptance.rs
@@ -74,6 +74,7 @@ async fn teensylc_blink_meets_205_acceptance_criteria() {
         extra_build_flags: Vec::new(),
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let result =
diff --git a/crates/fbuild-cli/src/cli/build.rs b/crates/fbuild-cli/src/cli/build.rs
index e9a4f9ce6..c63e277ad 100644
--- a/crates/fbuild-cli/src/cli/build.rs
+++ b/crates/fbuild-cli/src/cli/build.rs
@@ -120,6 +120,7 @@ pub async fn run_build(
         output_dir,
         pio_env: daemon_client::capture_pio_env(),
         bloat_analysis,
+        caller_path: daemon_client::capture_caller_path(),
     };
 
     let stream_start = std::time::Instant::now();
diff --git a/crates/fbuild-cli/src/cli/clean.rs b/crates/fbuild-cli/src/cli/clean.rs
index 9a7a30905..1a089ab11 100644
--- a/crates/fbuild-cli/src/cli/clean.rs
+++ b/crates/fbuild-cli/src/cli/clean.rs
@@ -59,6 +59,7 @@ pub async fn run_clean(
         output_dir: None,
         pio_env: daemon_client::capture_pio_env(),
         bloat_analysis: false,
+        caller_path: daemon_client::capture_caller_path(),
     };
 
     let response = client.build_streaming(&req).await?;
diff --git a/crates/fbuild-cli/src/cli/deploy.rs b/crates/fbuild-cli/src/cli/deploy.rs
index 227151fa8..59efeb187 100644
--- a/crates/fbuild-cli/src/cli/deploy.rs
+++ b/crates/fbuild-cli/src/cli/deploy.rs
@@ -222,6 +222,7 @@ pub async fn run_deploy(
         output_dir,
         pio_env: daemon_client::capture_pio_env(),
         usb_recovery_policy,
+        caller_path: daemon_client::capture_caller_path(),
     };
 
     let resp = client.deploy(&req).await?;
diff --git a/crates/fbuild-cli/src/daemon_client.rs b/crates/fbuild-cli/src/daemon_client.rs
index 07903721f..5c5fb00e7 100644
--- a/crates/fbuild-cli/src/daemon_client.rs
+++ b/crates/fbuild-cli/src/daemon_client.rs
@@ -1014,6 +1014,12 @@ where
     })
 }
 
+/// Snapshot the calling CLI's PATH for per-request forwarding so the daemon
+/// can resolve bare-name tool spawns against it (FastLED/fbuild#1219).
+pub(crate) fn capture_caller_path() -> Option<String> {
+    launcher_path(std::env::vars_os()).map(|p| p.to_string_lossy().into_owned())
+}
+
 /// Spawn a single daemon process instance.
 async fn spawn_daemon_process() -> fbuild_core::Result<()> {
     // FastLED/fbuild#830: prefer a `fbuild-daemon` binary sitting next
diff --git a/crates/fbuild-cli/src/daemon_client/types.rs b/crates/fbuild-cli/src/daemon_client/types.rs
index ddb136d87..dfdeb9d5b 100644
--- a/crates/fbuild-cli/src/daemon_client/types.rs
+++ b/crates/fbuild-cli/src/daemon_client/types.rs
@@ -55,6 +55,10 @@ pub struct BuildRequest {
     /// See FastLED/fbuild#594.
     #[serde(default)]
     pub bloat_analysis: bool,
+    /// Snapshot of the caller's PATH so the daemon resolves bare-name tool
+    /// spawns against it instead of its own stale PATH (FastLED/fbuild#1219).
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub caller_path: Option<String>,
 }
 
 /// `POST /api/install-deps` request. Mirrors
@@ -138,6 +142,10 @@ pub struct DeployRequest {
     /// intentionally non-elevating; #1147 is the first daemon consumer.
     #[serde(default, skip_serializing_if = "is_default_usb_recovery_policy")]
     pub usb_recovery_policy: fbuild_core::usb::UsbRecoveryPolicy,
+    /// Snapshot of the caller's PATH so the daemon resolves bare-name tool
+    /// spawns against it instead of its own stale PATH (FastLED/fbuild#1219).
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub caller_path: Option<String>,
 }
 
 fn is_default_usb_recovery_policy(policy: &fbuild_core::usb::UsbRecoveryPolicy) -> bool {
diff --git a/crates/fbuild-cli/src/mcp/tools.rs b/crates/fbuild-cli/src/mcp/tools.rs
index 116d59e67..e6eff73f3 100644
--- a/crates/fbuild-cli/src/mcp/tools.rs
+++ b/crates/fbuild-cli/src/mcp/tools.rs
@@ -122,6 +122,7 @@ pub(super) async fn execute_tool(
                 output_dir: None,
                 pio_env: crate::daemon_client::capture_pio_env(),
                 bloat_analysis: false,
+                caller_path: crate::daemon_client::capture_caller_path(),
             };
 
             let resp = client
@@ -189,6 +190,7 @@ pub(super) async fn execute_tool(
                 output_dir: None,
                 pio_env: crate::daemon_client::capture_pio_env(),
                 usb_recovery_policy: fbuild_core::usb::UsbRecoveryPolicy::Default,
+                caller_path: crate::daemon_client::capture_caller_path(),
             };
 
             let resp = client
diff --git a/crates/fbuild-core/src/subprocess.rs b/crates/fbuild-core/src/subprocess.rs
index 7ffcff960..070ad4233 100644
--- a/crates/fbuild-core/src/subprocess.rs
+++ b/crates/fbuild-core/src/subprocess.rs
@@ -660,9 +660,7 @@ fn compute_env(program: &str, overlay: Option<&[(&str, &str)]>) -> Option<Vec<(S
         }
 
         if let Some(vars) = overlay {
-            for (k, v) in vars {
-                env_map.insert((*k).to_string(), (*v).to_string());
-            }
+            apply_overlay_windows(&mut env_map, vars);
         }
 
         Some(env_map.into_iter().collect())
@@ -684,6 +682,41 @@ fn compute_env(program: &str, overlay: Option<&[(&str, &str)]>) -> Option<Vec<(S
     }
 }
 
+/// Merge an env overlay into the Windows env map.
+///
+/// Windows env keys are case-insensitive but the map here is not:
+/// remove any case-variant of the overlay key first, otherwise an
+/// overlay "PATH" coexists with the inherited "Path" and the child's
+/// last-insert-wins env map silently keeps the inherited value
+/// (FastLED/fbuild#1219).
+#[cfg(windows)]
+fn apply_overlay_windows(
+    env_map: &mut std::collections::BTreeMap<String, String>,
+    vars: &[(&str, &str)],
+) {
+    for (k, v) in vars {
+        env_map.retain(|existing, _| !existing.eq_ignore_ascii_case(k));
+        env_map.insert((*k).to_string(), (*v).to_string());
+    }
+}
+
+/// PATH overlay for a bare-name program spawn: when `program` has no
+/// path separator and a caller PATH snapshot is available, resolve the
+/// spawn against the caller's PATH instead of the daemon's. Absolute
+/// or relative-path programs never need it.
+pub fn bare_name_path_overlay<'a>(
+    program: &str,
+    caller_path: Option<&'a str>,
+) -> Option<[(&'static str, &'a str); 1]> {
+    if program.contains('/') || program.contains('\\') {
+        return None;
+    }
+    match caller_path {
+        Some(p) if !p.is_empty() => Some([("PATH", p)]),
+        _ => None,
+    }
+}
+
 #[cfg(windows)]
 fn is_msys_environment(env_map: &std::collections::BTreeMap<String, String>) -> bool {
     env_map.contains_key("MSYSTEM") || env_map.contains_key("MSYS")
@@ -993,6 +1026,146 @@ mod tests {
         assert!(result.stdout.trim().contains("no-timeout"));
     }
 
+    // FastLED/fbuild#1219: a caller-supplied PATH overlay must replace
+    // the inherited Windows "Path" entry, not coexist with it — the
+    // Command env map is case-insensitive last-insert-wins, so a
+    // duplicate lets the daemon's stale Path silently win.
+    #[cfg(windows)]
+    #[test]
+    fn path_overlay_replaces_inherited_path_case_insensitively() {
+        let env = compute_env("esptool", Some(&[("PATH", "X-marker")]))
+            .expect("windows always returns a full env vector");
+        let path_entries: Vec<&(String, String)> = env
+            .iter()
+            .filter(|(k, _)| k.eq_ignore_ascii_case("path"))
+            .collect();
+        assert_eq!(
+            path_entries.len(),
+            1,
+            "exactly one PATH-ish key expected, got {path_entries:?}"
+        );
+        assert_eq!(path_entries[0].1, "X-marker");
+    }
+
+    // Deterministic form of the #1219 regression: the test process env
+    // may already spell the key "PATH" (bash/soldr do), which masks the
+    // duplicate-key bug in the end-to-end test above. Seed the map with
+    // the Windows-typical "Path" casing explicitly.
+    #[cfg(windows)]
+    #[test]
+    fn path_overlay_wins_over_differently_cased_inherited_key() {
+        let mut env_map = std::collections::BTreeMap::new();
+        env_map.insert("Path".to_string(), "stale-daemon-path".to_string());
+        apply_overlay_windows(&mut env_map, &[("PATH", "X-marker")]);
+
+        let path_entries: Vec<(&String, &String)> = env_map
+            .iter()
+            .filter(|(k, _)| k.eq_ignore_ascii_case("path"))
+            .collect();
+        assert_eq!(
+            path_entries.len(),
+            1,
+            "exactly one PATH-ish key expected, got {path_entries:?}"
+        );
+        assert_eq!(path_entries[0].1, "X-marker");
+    }
+
+    #[test]
+    fn bare_name_path_overlay_applies_only_to_bare_names() {
+        assert_eq!(
+            bare_name_path_overlay("esptool", Some("C:\\caller\\bin")),
+            Some([("PATH", "C:\\caller\\bin")])
+        );
+        assert_eq!(
+            bare_name_path_overlay("C:\\tools\\esptool.exe", Some("C:\\caller\\bin")),
+            None
+        );
+        assert_eq!(
+            bare_name_path_overlay("tools/esptool", Some("C:\\caller\\bin")),
+            None
+        );
+        assert_eq!(bare_name_path_overlay("esptool", None), None);
+        assert_eq!(bare_name_path_overlay("esptool", Some("")), None);
+    }
+
+    /// End-to-end proof for FastLED/fbuild#1219: a PATH overlay must make
+    /// `run_command` resolve a bare executable name from the overlay's
+    /// directory — not just produce the right `("PATH", …)` tuple. Uses a
+    /// uniquely named probe executable staged into a TempDir so ambient
+    /// PATH can never satisfy the lookup.
+    #[tokio::test]
+    async fn run_command_resolves_bare_name_from_overlay_path() {
+        let tmp = tempfile::tempdir().expect("tempdir");
+        let dir = tmp.path();
+
+        #[cfg(windows)]
+        let probe_path = {
+            let system_root = std::env::var("SystemRoot").expect("SystemRoot must be set");
+            let src = Path::new(&system_root).join("System32").join("cmd.exe");
+            let dst = dir.join("fbuild_1219_probe.exe");
+            std::fs::copy(&src, &dst).expect("copy cmd.exe into overlay dir");
+            dst
+        };
+        #[cfg(unix)]
+        let probe_path = {
+            use std::os::unix::fs::PermissionsExt;
+            let dst = dir.join("fbuild_1219_probe");
+            std::fs::write(&dst, "#!/bin/sh\necho overlay-marker\n").expect("write probe script");
+            std::fs::set_permissions(&dst, std::fs::Permissions::from_mode(0o755))
+                .expect("chmod probe script");
+            dst
+        };
+
+        let dir_str = dir.to_string_lossy();
+        let overlay = [("PATH", dir_str.as_ref())];
+        let bare_args: Vec<&str> = if cfg!(windows) {
+            vec!["fbuild_1219_probe", "/C", "echo overlay-marker"]
+        } else {
+            vec!["fbuild_1219_probe"]
+        };
+
+        // Bare name + overlay → resolved from the overlay PATH.
+        let result = run_command(
+            &bare_args,
+            None,
+            Some(&overlay),
+            Some(Duration::from_secs(30)),
+        )
+        .await
+        .expect("bare-name spawn must resolve via the overlay PATH");
+        assert!(result.success(), "got: {result:?}");
+        assert!(
+            result.stdout.contains("overlay-marker"),
+            "stdout was {:?}",
+            result.stdout
+        );
+
+        // Absolute path, no overlay → normal operation is unaffected.
+        let probe_str = probe_path.to_string_lossy();
+        let abs_args: Vec<&str> = if cfg!(windows) {
+            vec![probe_str.as_ref(), "/C", "echo overlay-marker"]
+        } else {
+            vec![probe_str.as_ref()]
+        };
+        let result = run_command(&abs_args, None, None, Some(Duration::from_secs(30)))
+            .await
+            .expect("absolute-path spawn works without any overlay");
+        assert!(result.success(), "got: {result:?}");
+        assert!(
+            result.stdout.contains("overlay-marker"),
+            "stdout was {:?}",
+            result.stdout
+        );
+
+        // Bare name WITHOUT the overlay → not on ambient PATH → spawn
+        // fails, proving the first resolution came from the overlay.
+        let result = run_command(&bare_args, None, None, Some(Duration::from_secs(30))).await;
+        assert!(
+            result.is_err(),
+            "bare name must not resolve from ambient PATH: {result:?}"
+        );
+    }
+
     #[tokio::test]
     async fn run_command_with_stdin_pipes_payload() {
         // Round-trip: feed stdin → expect it back on stdout. `cat` on
diff --git a/crates/fbuild-daemon/src/handlers/emulator/select.rs b/crates/fbuild-daemon/src/handlers/emulator/select.rs
index 4c9ddb612..ff05ee576 100644
--- a/crates/fbuild-daemon/src/handlers/emulator/select.rs
+++ b/crates/fbuild-daemon/src/handlers/emulator/select.rs
@@ -323,6 +323,7 @@ pub async fn test_emu(
             },
             watch_set_cache: Some(std::sync::Arc::clone(&ctx.watch_set_cache) as std::sync::Arc<_>),
             bloat_analysis: false,
+            caller_path: None,
         };
 
         let p = platform;
diff --git a/crates/fbuild-daemon/src/handlers/emulator/tests_process.rs b/crates/fbuild-daemon/src/handlers/emulator/tests_process.rs
index ad21d33b7..2364a49c4 100644
--- a/crates/fbuild-daemon/src/handlers/emulator/tests_process.rs
+++ b/crates/fbuild-daemon/src/handlers/emulator/tests_process.rs
@@ -149,6 +149,7 @@ async fn run_real_esp32s3_fixture_in_qemu() {
         ],
         watch_set_cache: None,
         bloat_analysis: false,
+        caller_path: None,
     };
 
     let orchestrator = fbuild_build::esp32::orchestrator::Esp32Orchestrator;
diff --git a/crates/fbuild-daemon/src/handlers/operations/build.rs b/crates/fbuild-daemon/src/handlers/operations/build.rs
index 05a45f254..4d70fd8e6 100644
--- a/crates/fbuild-daemon/src/handlers/operations/build.rs
+++ b/crates/fbuild-daemon/src/handlers/operations/build.rs
@@ -237,6 +237,20 @@ pub async fn build(
         .as_deref()
         .map(|p| resolve_client_path(p, req.caller_cwd.as_deref(), &project_dir));
 
+    // FastLED/fbuild#1219: surface PATH drift between the caller and the
+    // daemon — bare-name tool spawns resolve against the caller's PATH.
+    if let Some(caller_path) = req.caller_path.as_deref() {
+        let daemon_path = std::env::var("PATH").unwrap_or_default();
+        if caller_path != daemon_path {
+            tracing::info!(
+                "caller PATH differs from daemon PATH (caller {} chars, daemon {} chars); \
+                 bare-name tools resolve against the caller's (see #1219)",
+                caller_path.len(),
+                daemon_path.len()
+            );
+        }
+    }
+
     if stream {
         // --- STREAMING PATH ---
         // Build runs in a background task; log lines stream to client as NDJSON.
@@ -281,6 +295,7 @@ pub async fn build(
             extra_build_flags: Vec::new(),
             watch_set_cache: Some(Arc::clone(&ctx.watch_set_cache) as Arc<_>),
             bloat_analysis: req.bloat_analysis,
+            caller_path: req.caller_path.clone(),
         };
 
         let project_dir_desc = req.project_dir.clone();
@@ -726,6 +741,7 @@ pub async fn build(
             extra_build_flags: Vec::new(),
             watch_set_cache: Some(Arc::clone(&ctx.watch_set_cache) as Arc<_>),
             bloat_analysis: req.bloat_analysis,
+            caller_path: req.caller_path,
         };
 
         // fbuild#813 / #815: orchestrator.build is async, call directly.
diff --git a/crates/fbuild-daemon/src/handlers/operations/deploy.rs b/crates/fbuild-daemon/src/handlers/operations/deploy.rs
index f87f0ba48..d22a57a1c 100644
--- a/crates/fbuild-daemon/src/handlers/operations/deploy.rs
+++ b/crates/fbuild-daemon/src/handlers/operations/deploy.rs
@@ -252,6 +252,7 @@ pub async fn deploy(
             },
             watch_set_cache: Some(Arc::clone(&ctx.watch_set_cache) as Arc<_>),
             bloat_analysis: false,
+            caller_path: req.caller_path.clone(),
         };
 
         // fbuild#813: orchestrator.build is now async — call directly,
diff --git a/crates/fbuild-daemon/src/models.rs b/crates/fbuild-daemon/src/models.rs
index 206de45d8..8e2264bee 100644
--- a/crates/fbuild-daemon/src/models.rs
+++ b/crates/fbuild-daemon/src/models.rs
@@ -81,6 +81,10 @@ pub struct BuildRequest {
     /// See FastLED/fbuild#594.
     #[serde(default)]
     pub bloat_analysis: bool,
+    /// Snapshot of the caller's PATH so bare-name tool spawns resolve
+    /// against it instead of the daemon's stale PATH (FastLED/fbuild#1219).
+    #[serde(default)]
+    pub caller_path: Option<String>,
 }
 
 /// POST /api/deploy
@@ -149,6 +153,10 @@ pub struct DeployRequest {
     /// daemon remains unprivileged and merely carries this typed policy.
     #[serde(default)]
     pub usb_recovery_policy: fbuild_core::usb::UsbRecoveryPolicy,
+    /// Snapshot of the caller's PATH so bare-name tool spawns resolve
+    /// against it instead of the daemon's stale PATH (FastLED/fbuild#1219).
+    #[serde(default)]
+    pub caller_path: Option<String>,
 }
 
 fn default_qemu_timeout() -> u32 {
@@ -668,6 +676,39 @@ mod tests {
         assert_eq!(req.src_dir.unwrap(), "examples/AutoResearch");
     }
 
+    // --- caller_path forwarding (FastLED/fbuild#1219) ---
+
+    #[test]
+    fn build_request_caller_path_defaults_to_none() {
+        let json = r#"{"project_dir": "/tmp/p"}"#;
+        let req: BuildRequest = serde_json::from_str(json).unwrap();
+        assert!(req.caller_path.is_none());
+    }
+
+    #[test]
+    fn build_request_caller_path_round_trips() {
+        let json = r#"{"project_dir": "/tmp/p", "caller_path": "C:\\venv\\Scripts;C:\\bin"}"#;
+        let req: BuildRequest = serde_json::from_str(json).unwrap();
+        assert_eq!(
+            req.caller_path.as_deref(),
+            Some("C:\\venv\\Scripts;C:\\bin")
+        );
+    }
+
+    #[test]
+    fn deploy_request_caller_path_defaults_to_none() {
+        let json = r#"{"project_dir": "/tmp/p"}"#;
+        let req: DeployRequest = serde_json::from_str(json).unwrap();
+        assert!(req.caller_path.is_none());
+    }
+
+    #[test]
+    fn deploy_request_caller_path_round_trips() {
+        let json = r#"{"project_dir": "/tmp/p", "caller_path": "/opt/venv/bin:/usr/bin"}"#;
+        let req: DeployRequest = serde_json::from_str(json).unwrap();
+        assert_eq!(req.caller_path.as_deref(), Some("/opt/venv/bin:/usr/bin"));
+    }
+
     #[test]
     fn build_request_with_request_id() {
         let json = r#"{"project_dir": "/tmp/p", "request_id": "abc-123"}"#;