diff --git a/esphome/arduino8266/toolchain.py b/esphome/arduino8266/toolchain.py
index 1cb8d32436..1cc26396e1 100644
--- a/esphome/arduino8266/toolchain.py
+++ b/esphome/arduino8266/toolchain.py
@@ -107,7 +107,11 @@ def run_compile(config: ConfigType, verbose: bool) -> int:
         return rc
 
     _print_size_summary(build_dir)
-    get_idedata()
+    if get_idedata() is None:
+        _LOGGER.warning(
+            "Could not generate idedata from %s",
+            build_dir / "compile_commands.json",
+        )
     return 0
 
 
@@ -218,7 +222,9 @@ def get_idedata() -> dict | None:
     return load_or_build_idedata(
         get_build_dir() / "compile_commands.json",
         get_elf_path(),
-        CORE.relative_internal_path("idedata", f"{CORE.name}.json"),
+        # Suffixed so a platformio->arduino->platformio round trip on one
+        # config never serves the other toolchain's cache shape
+        CORE.relative_internal_path("idedata", f"{CORE.name}.arduino.json"),
         # The compile DB's commands carry the same ccache prefix the ninja
         # rules were generated with
         launcher=str(ccache) if ccache else None,
diff --git a/esphome/components/esp8266/__init__.py b/esphome/components/esp8266/__init__.py
index 21cec7d4ae..7afa1b1f9c 100644
--- a/esphome/components/esp8266/__init__.py
+++ b/esphome/components/esp8266/__init__.py
@@ -1,9 +1,10 @@
-import functools
 import logging
+import math
 from pathlib import Path
 import platform
 import re
 import subprocess
+import time
 
 import esphome.codegen as cg
 import esphome.config_validation as cv
@@ -603,10 +604,21 @@ ESP8266_EXCEPTION_CODES = {
 }
 
 
-@functools.cache
-def _warn_missing_decode_tool(path: str) -> None:
-    # Cached so a stack dump of dozens of addresses warns once, not per line
-    _LOGGER.warning("Cannot decode crash addresses: %s missing", path)
+_DECODE_WARNED_AT: dict[str, float] = {}
+
+
+def _warn_decode_problem(key: str, message: str, *args) -> None:
+    """Warn, deduplicated per stack dump but not per process.
+
+    A dump decodes dozens of addresses in a burst; one warning per burst is
+    enough. A long-running dashboard must still warn on the next dump, so
+    the suppression expires instead of living for the process lifetime.
+    """
+    now = time.monotonic()
+    if now - _DECODE_WARNED_AT.get(key, -math.inf) < 30:
+        return
+    _DECODE_WARNED_AT[key] = now
+    _LOGGER.warning(message, *args)
 
 
 def _decode_pc(config, addr):
@@ -617,7 +629,9 @@ def _decode_pc(config, addr):
         elf = native_toolchain.get_elf_path()
         missing = addr2line if not addr2line.is_file() else elf
         if not missing.is_file():
-            _warn_missing_decode_tool(str(missing))
+            _warn_decode_problem(
+                str(missing), "Cannot decode crash addresses: %s missing", missing
+            )
             return
         addr2line, elf = str(addr2line), str(elf)
     else:
@@ -632,6 +646,12 @@ def _decode_pc(config, addr):
     try:
         translation = subprocess.check_output(command, close_fds=False).decode().strip()
     except Exception:  # noqa: BLE001  # pylint: disable=broad-except
+        if CORE.using_toolchain_arduino:
+            # A present-but-failing addr2line (stale ELF, bad install) must
+            # be visible, matching the missing-tool warning above
+            _warn_decode_problem(
+                "addr2line-failed", "Could not decode crash address %s", addr
+            )
         _LOGGER.debug("Caught exception for command %s", command, exc_info=1)
         return
 
diff --git a/tests/unit_tests/components/esp8266/test_toolchain_validation.py b/tests/unit_tests/components/esp8266/test_toolchain_validation.py
index a5e41c28a0..188169efb1 100644
--- a/tests/unit_tests/components/esp8266/test_toolchain_validation.py
+++ b/tests/unit_tests/components/esp8266/test_toolchain_validation.py
@@ -122,7 +122,7 @@ def test_decode_pc_native_missing_tools_warns_once(
     """A stack dump of many addresses produces one missing-tool warning."""
     from esphome.components import esp8266
 
-    esp8266._warn_missing_decode_tool.cache_clear()
+    esp8266._DECODE_WARNED_AT.clear()
     with (
         patch(
             "esphome.arduino8266.toolchain.get_addr2line_path",
@@ -136,4 +136,13 @@ def test_decode_pc_native_missing_tools_warns_once(
         esp8266._decode_pc({}, "40201234")
         esp8266._decode_pc({}, "40201238")
     assert caplog.text.count("Cannot decode crash addresses") == 1
-    esp8266._warn_missing_decode_tool.cache_clear()
+    esp8266._DECODE_WARNED_AT.clear()
+
+
+def test_resolve_toolchain_rejects_unsupported() -> None:
+    """ESP8266 rejects a CLI toolchain it cannot serve, like every platform."""
+    from esphome.components.esp8266 import _resolve_toolchain
+
+    CORE.toolchain = Toolchain.SDK_NRF
+    with pytest.raises(cv.Invalid, match="Unsupported toolchain 'sdk-nrf'"):
+        _resolve_toolchain({})
diff --git a/tests/unit_tests/test_arduino8266_toolchain.py b/tests/unit_tests/test_arduino8266_toolchain.py
index 06f8c199f9..28e4128de4 100644
--- a/tests/unit_tests/test_arduino8266_toolchain.py
+++ b/tests/unit_tests/test_arduino8266_toolchain.py
@@ -212,7 +212,7 @@ def test_get_idedata_delegates(tmp_path: Path) -> None:
     compile_commands, elf, cache = mock_load.call_args[0]
     assert compile_commands.name == "compile_commands.json"
     assert elf.name == "firmware.elf"
-    assert cache.name == "test8266.json"
+    assert cache.name == "test8266.arduino.json"
     # The exact configured launcher is passed for compile DB parsing
     assert mock_load.call_args.kwargs["launcher"] == str(Path("/cc/ccache"))