size gate: emit flash_bytes from ELF for targets without a packaged .bin (#10940)

* size gate: emit flash_bytes from ELF for targets without a packaged .bin

nRF52 builds package hex/uf2/DFU zip but no raw .bin, so collect_sizes.py
dropped budgeted envs like rak4631 entirely and the size-budget-gate failed
closed. Emit ELF text+data as flash_bytes in the manifest and use it as the
fallback flash measurement.

* Factor shared size-tool invocation into run_size_tool helper

bin/platformio-custom.py

@@ -45,6 +45,27 @@ def infer_architecture(board_cfg):
         return "stm32"
     return None
 
+def run_size_tool(env, flag, purpose):
+    """Run the toolchain size tool against the built ELF and return its output.
+
+    Shared plumbing for compute_ram_bytes / compute_flash_bytes. Returns None
+    when the ELF is missing or the tool fails; the manifest then simply omits
+    the metric and downstream size reports show "n/a".
+    """
+    elf = env.File(env.subst("$BUILD_DIR/${PROGNAME}.elf"))
+    if not elf.exists():
+        return None
+    size_tool = env.subst("$SIZETOOL") or "size"
+    try:
+        return subprocess.check_output(
+            [size_tool, flag, elf.get_abspath()],
+            env=env["ENV"],
+            universal_newlines=True,
+        )
+    except Exception as exc:
+        print(f"mtjson: skipping {purpose} ({size_tool} failed: {exc})")
+        return None
+
 def compute_ram_bytes(env):
     """Static RAM usage (.data + .bss) of the ELF, via the toolchain size tool.
 
@@ -54,18 +75,8 @@ def compute_ram_bytes(env):
     Returns None when the value cannot be determined; the manifest then simply
     omits ram_bytes and downstream size reports show "n/a".
     """
-    elf = env.File(env.subst("$BUILD_DIR/${PROGNAME}.elf"))
-    if not elf.exists():
-        return None
-    size_tool = env.subst("$SIZETOOL") or "size"
-    try:
-        output = subprocess.check_output(
-            [size_tool, "-A", elf.get_abspath()],
-            env=env["ENV"],
-            universal_newlines=True,
-        )
-    except Exception as exc:
-        print(f"mtjson: skipping ram_bytes ({size_tool} failed: {exc})")
+    output = run_size_tool(env, "-A", "ram_bytes")
+    if output is None:
         return None
     ram = 0
     found = False
@@ -88,6 +99,24 @@ def compute_ram_bytes(env):
                 continue
     return ram if found else None
 
+def compute_flash_bytes(env):
+    """Flash footprint (text + data) of the ELF via the toolchain size tool.
+
+    Approximates the flashed app image for targets whose packaged artifacts do
+    not include a raw .bin (e.g. nRF52: hex/uf2/DFU zip only); consumed by
+    bin/collect_sizes.py as a fallback flash measurement for the size report
+    and the bin/ram_budgets.json budget gate. Returns None when the value
+    cannot be determined; the manifest then simply omits flash_bytes.
+    """
+    output = run_size_tool(env, "-B", "flash_bytes")
+    if output is None:
+        return None
+    for line in output.splitlines():
+        parts = line.split()
+        if len(parts) >= 3 and parts[0].isdigit() and parts[1].isdigit():
+            return int(parts[0]) + int(parts[1])
+    return None
+
 def manifest_gather(source, target, env):
     global manifest_ran
     if manifest_ran:
@@ -141,9 +170,9 @@ def manifest_gather(source, target, env):
                 d["part_name"] = partition_map[p]
             out.append(d)
             print(d)
-    manifest_write(out, env, compute_ram_bytes(env))
+    manifest_write(out, env, compute_ram_bytes(env), compute_flash_bytes(env))
 
-def manifest_write(files, env, ram_bytes=None):
+def manifest_write(files, env, ram_bytes=None, flash_bytes=None):
     # Defensive: also skip manifest writing if we cannot determine architecture
     def get_project_option(name):
         try:
@@ -184,6 +213,10 @@ def manifest_write(files, env, ram_bytes=None):
     # the CI size report and the bin/ram_budgets.json budget gate.
     if ram_bytes is not None:
         manifest["ram_bytes"] = ram_bytes
+    # Flash footprint (text + data); fallback flash measurement for targets
+    # whose packaged artifacts include no raw .bin (e.g. nRF52).
+    if flash_bytes is not None:
+        manifest["flash_bytes"] = flash_bytes
     # Get partition table (generated in esp32_pre.py) if it exists
     if env.get("custom_mtjson_part"):
         # custom_mtjson_part is a JSON string, convert it back to a dict