diff --git a/README.md b/README.md
index 58022c9e..15501b5c 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,8 @@
 [![Documentation](https://github.com/fastled/fbuild/actions/workflows/docs.yml/badge.svg)](https://github.com/fastled/fbuild/actions/workflows/docs.yml)
 [![Validate Boards](https://github.com/fastled/fbuild/actions/workflows/validate-boards.yml/badge.svg)](https://github.com/fastled/fbuild/actions/workflows/validate-boards.yml)
 [![Build Native Binaries](https://github.com/fastled/fbuild/actions/workflows/build.yml/badge.svg)](https://github.com/fastled/fbuild/actions/workflows/build.yml)
+[![Library Selection Acceptance (#205)](https://github.com/fastled/fbuild/actions/workflows/acceptance-205.yml/badge.svg)](https://github.com/fastled/fbuild/actions/workflows/acceptance-205.yml)
+[![Library Selection Perf (#205)](https://github.com/fastled/fbuild/actions/workflows/bench-205.yml/badge.svg)](https://github.com/fastled/fbuild/actions/workflows/bench-205.yml)
 
 <details>
 <summary><strong>Per-platform board build badges</strong> (click to expand)</summary>
diff --git a/crates/fbuild-build/tests/teensylc_acceptance.rs b/crates/fbuild-build/tests/teensylc_acceptance.rs
index 3c5bd6d7..50f6a7fa 100644
--- a/crates/fbuild-build/tests/teensylc_acceptance.rs
+++ b/crates/fbuild-build/tests/teensylc_acceptance.rs
@@ -30,7 +30,10 @@ fn teensylc_blink_meets_205_acceptance_criteria() {
 
     let params = BuildParams {
         project_dir: project_dir.clone(),
-        env_name: "teensyLC".to_string(),
+        // WHY: env names are case-sensitive and must match the
+        // [env:teensylc] key in tests/platform/teensylc/platformio.ini.
+        // Same root-cause family as #220 / #221 in measure_baseline_205.py.
+        env_name: "teensylc".to_string(),
         clean: true,
         profile: BuildProfile::Release,
         build_dir: build_dir.path().to_path_buf(),
@@ -71,15 +74,29 @@ fn teensylc_blink_meets_205_acceptance_criteria() {
              #204 regression"
         );
     }
-    for required in ["setup", "loop"] {
+    // WHY: setup/loop are extern "C" via Arduino.h's prototype, so
+    // ideally appear unmangled. But Teensyduino's main calls them via
+    // the framework's main.cpp and toolchain LTO can leave only the
+    // mangled C++ symbols (`_Z5setupv` / `_Z4loopv`) when the .ino is
+    // compiled as C++ without the extern "C" prototype reaching the
+    // definition. Accept either form — the contract is "the user's
+    // setup/loop landed in the firmware", not "they kept their C
+    // linkage". The earlier `has_symbol_containing` was rejected in
+    // PR #209 review for matching `Stream::setupXxx`-style false
+    // positives; the explicit-mangled fallback below is targeted and
+    // doesn't share that problem.
+    for (required, mangled) in [("setup", "_Z5setupv"), ("loop", "_Z4loopv")] {
+        let unmangled_present = probe.has_symbol(required).expect("symbol query");
+        let mangled_present = probe.has_symbol(mangled).expect("symbol query");
         assert!(
-            probe.has_symbol(required).expect("symbol query"),
-            "A-11: required symbol '{required}' missing from ELF"
+            unmangled_present || mangled_present,
+            "A-11: required symbol '{required}' missing from ELF \
+             (also looked for mangled '{mangled}')"
         );
     }
 
     // ── compile_commands.json probes (AC#1, A-20..A-22) ─────────────────
-    let compdb_path = locate_compile_commands(build_dir.path(), "teensyLC")
+    let compdb_path = locate_compile_commands(build_dir.path(), "teensylc")
         .expect("compile_commands.json should land in build dir");
     let db = CompileDb::from_path(&compdb_path).expect("parse compile_commands.json");
     assert!(
diff --git a/crates/fbuild-library-select/src/lib.rs b/crates/fbuild-library-select/src/lib.rs
index 8e049558..ddd4d53a 100644
--- a/crates/fbuild-library-select/src/lib.rs
+++ b/crates/fbuild-library-select/src/lib.rs
@@ -248,6 +248,48 @@ mod tests {
         );
     }
 
+    #[test]
+    fn r04_pass2_reconciliation_catches_cpp_only_dependency() {
+        // The whole reason the LDF resolver is 2-pass instead of single-pass
+        // BFS: a lib's `.cpp` may pull in a second lib that the first lib's
+        // `.h` does NOT mention. Pass 1 (BFS from project seeds + reached
+        // headers) cannot see that edge; pass 2 re-seeds with each selected
+        // lib's full source set and catches it.
+        //
+        // Setup: project includes <SPI.h>. SPI.h is silent. SPI.cpp includes
+        // <Wire.h>. Wire is only reachable through SPI.cpp.
+        //
+        // Expected: pass 1 selects {SPI}; pass 2 (with SPI.cpp as a seed)
+        // selects {SPI, Wire}. A regression that drops the second pass would
+        // produce {SPI} only and silently miss Wire at link time.
+        let tmp = TempDir::new().unwrap();
+        let project_src = tmp.path().join("project").join("src");
+        write(&project_src.join("main.cpp"), "#include <SPI.h>\n");
+
+        let mut spi = lib(tmp.path(), "SPI");
+        write(
+            &spi.include_dirs[0].join("SPI.h"),
+            "// no transitive includes\n",
+        );
+        let spi_cpp = spi.include_dirs[0].join("SPI.cpp");
+        write(&spi_cpp, "#include <Wire.h>\n");
+        spi.source_files.push(spi_cpp);
+
+        let mut wire = lib(tmp.path(), "Wire");
+        write(&wire.include_dirs[0].join("Wire.h"), "");
+        let wire_cpp = wire.include_dirs[0].join("Wire.cpp");
+        write(&wire_cpp, "");
+        wire.source_files.push(wire_cpp);
+
+        let seeds = vec![project_src.join("main.cpp")];
+        let sel = resolve(&seeds, &[project_src], &[spi, wire]);
+        assert_eq!(
+            sel.required_libraries,
+            vec!["SPI".to_string(), "Wire".to_string()],
+            "pass 2 reconciliation must catch Wire reached only via SPI.cpp"
+        );
+    }
+
     #[test]
     fn r03_no_includes_selects_nothing() {
         let tmp = TempDir::new().unwrap();