Warn and drop the broken healthcheck.start_interval mapping

newsfragments/start_interval_unsupported.bugfix

@@ -0,0 +1 @@
+Stop translating Compose `healthcheck.start_interval` to the unrelated Podman `--health-startup-interval` flag (which belongs to a separate startup-healthcheck mechanism). The field is now reported as unsupported with a warning until Podman gains a native equivalent (containers/podman#26505). Fixes #1500.

podman_compose.py

@@ -1574,15 +1574,30 @@ async def container_to_args(
         else:
             raise ValueError("'healthcheck.test' either a string or a list")
 
-    # interval, timeout, start_period, and start_interval are specified as durations.
+    # interval, timeout, and start_period are specified as durations.
     if "interval" in healthcheck:
         podman_args.extend(["--health-interval", healthcheck["interval"]])
     if "timeout" in healthcheck:
         podman_args.extend(["--health-timeout", healthcheck["timeout"]])
     if "start_period" in healthcheck:
         podman_args.extend(["--health-start-period", healthcheck["start_period"]])
     if "start_interval" in healthcheck:
-        podman_args.extend(["--health-startup-interval", healthcheck["start_interval"]])
+        # The previous mapping translated start_interval to
+        # --health-startup-interval, but that Podman flag belongs to a
+        # separate startup-healthcheck mechanism gated by --health-startup-cmd
+        # (which podman-compose does not generate), so the Compose-spec
+        # semantics of start_interval were silently lost. Podman does not yet
+        # provide a direct equivalent (see containers/podman#26505), so warn
+        # the user and drop the broken mapping. Re-enable once the Podman
+        # native equivalent lands.
+        log.warning(
+            "Compose 'healthcheck.start_interval' is currently not supported "
+            "by podman-compose: Podman has no equivalent for the "
+            "startup-period interval yet (see containers/podman#26505); the "
+            "field %r is being ignored for service %r.",
+            healthcheck["start_interval"],
+            cnt.get("name", cnt.get("service_name", "?")),
+        )
 
     # convert other parameters to string
     if "retries" in healthcheck:

tests/unit/test_container_to_args.py

@@ -1189,7 +1189,6 @@ async def test_healthcheck_options(self) -> None:
             "timeout": "10s",
             "retries": "3",
             "start_period": "5s",
-            "start_interval": "6s",
         }
 
         args = await container_to_args(c, cnt)
@@ -1207,14 +1206,37 @@ async def test_healthcheck_options(self) -> None:
                 '10s',
                 '--health-start-period',
                 '5s',
-                '--health-startup-interval',
-                '6s',
                 '--health-retries',
                 '3',
                 "busybox",
             ],
         )
 
+    async def test_healthcheck_start_interval_warns_and_omits_podman_flag(self) -> None:
+        """``start_interval`` has no Podman equivalent yet (containers/podman#26505).
+
+        The old behaviour silently mapped it to ``--health-startup-interval``,
+        but that flag belongs to a different mechanism gated by
+        ``--health-startup-cmd`` (which podman-compose never emits), so the
+        Compose-spec semantics were lost. The current contract is: emit a
+        warning, do not pass any ``--health-startup-interval`` flag.
+        """
+        c = create_compose_mock()
+        cnt = get_minimal_container()
+        cnt["healthcheck"] = {
+            "test": ["CMD", "true"],
+            "start_interval": "1s",
+        }
+
+        with self.assertLogs("podman_compose", level="WARNING") as cm:
+            args = await container_to_args(c, cnt)
+
+        self.assertTrue(
+            any("start_interval" in msg for msg in cm.output),
+            f"expected a warning mentioning start_interval, got: {cm.output!r}",
+        )
+        self.assertNotIn("--health-startup-interval", args)
+
     @parameterized.expand([
         "",
         "container:ipc_test0_container",