fleetd #415: split coverage() feature-state wording by pattern-key fallback semantics

CompletionResolver.coverage() measured pattern coverage (how many profiles set
a key) but its 'off' wording read as feature state. That is false for
errorPattern: an unset errorPattern still runs the classification against the
built-in BACKEND_ERROR pattern (CompletionResolver.java:84), so the empty case
is not off.

Add CompletionResolver.UnsetMeaning (OFF / BUILT_IN_DEFAULT), a required
parameter every coverage() call must supply — no defaulted overload, so a
future third pattern key cannot compile without stating what unset means for
it. Fleetd.java now passes UnsetMeaning.OFF for exhaustedPattern (no fallback
exists) and UnsetMeaning.BUILT_IN_DEFAULT for errorPattern.

Tests: updated the three existing empty/full/partial cases to pass the new
parameter, corrected the one test that pinned the old (wrong) errorPattern
wording, and added a test that asserts the same empty-coverage input produces
different wording for the two keys.

fleetd/src/main/java/dev/ltms/fleet/Fleetd.java

@@ -380,8 +380,8 @@ public final class Fleetd {
                 .map(session -> exhaustedPatternsByProfile.get(session.profile()))
                 .orElse(null);
         log.info("backend-exhausted classification (CB-578 stage A): {}",
-                CompletionResolver.coverage("exhaustedPattern", cfg.profiles().keySet(),
-                        exhaustedPatternsByProfile.keySet()));
+                CompletionResolver.coverage("exhaustedPattern", CompletionResolver.UnsetMeaning.OFF,
+                        cfg.profiles().keySet(), exhaustedPatternsByProfile.keySet()));
         // fleetd #201 Unit 5: classify a completion-fallback scrape that matches a profile's
         // configured backend-error refusal (a credential outage, a provider 5xx) as a backend error
         // rather than handing it back as a real answer. Compiled once at startup, keyed by profile
@@ -401,8 +401,8 @@ public final class Fleetd {
         BackendErrorPatternLookup backendErrorPatterns = backendErrorPatternLookup(sessions::roster,
                 errorPatternsByProfile);
         log.info("backend-error classification (fleetd #201 Unit 5): {}",
-                CompletionResolver.coverage("errorPattern", cfg.profiles().keySet(),
-                        errorPatternsByProfile.keySet()));
+                CompletionResolver.coverage("errorPattern", CompletionResolver.UnsetMeaning.BUILT_IN_DEFAULT,
+                        cfg.profiles().keySet(), errorPatternsByProfile.keySet()));
         // CB-578 stage B: on a classification that actually wins, quarantine the exhausted profile's
         // CREDENTIAL — not the profile name — so a profile sharing that credential (e.g. two models
         // on one OpenAI account) is refused too, not just the one that happened to report it. Reads

fleetd/src/main/java/dev/ltms/fleet/inject/CompletionResolver.java

@@ -698,17 +698,47 @@ public final class CompletionResolver implements TurnListener {
     }
 
     /**
-     * Coverage summary for the CB-578 stage A exhausted-pattern classification, logged at startup
+     * What an unset pattern key means for the classification it configures (fleetd#415).
+     * {@code coverage()} cannot infer this from the key's name — the two keys it currently
+     * describes disagree on it, and a string comparison on the name would just move the same bug
+     * to a new spot — so every caller must state it explicitly.
+     */
+    public enum UnsetMeaning {
+        /** No fallback exists: a profile with no configured pattern truly has this classification off. */
+        OFF,
+        /** A built-in pattern applies when unset: the classification still runs for that profile. */
+        BUILT_IN_DEFAULT
+    }
+
+    /**
+     * Coverage summary for a fleetd#201/CB-578-style pattern-key classification, logged at startup
      * the way {@link dev.ltms.fleet.health.FleetHealthMonitor#coverage} is — so an operator can
      * see whether the classification is on, and for which profiles, without reading every
      * profile's config by hand.
      *
+     * <p>fleetd#415: this method measures <em>pattern coverage</em> — how many profiles set the
+     * key — which is not the same thing as <em>feature state</em> for a key with a fallback. For
+     * {@code errorPattern}, an empty {@code configuredProfiles} still runs the classification
+     * against {@code CompletionResolver}'s built-in compatibility pattern ({@link #BACKEND_ERROR}
+     * at line ~84); for {@code exhaustedPattern} there is no fallback, so empty really does mean
+     * off. {@code unsetMeaning} is the single, required source of that fact — see
+     * {@link dev.ltms.fleet.config.FleetConfig#rejectMalformedProfilePatterns} lines ~2029-2032 for
+     * where it is documented for config authors. It is a required parameter, not a defaulted
+     * overload: a third pattern key added later must supply one to compile at all, rather than
+     * silently inheriting whichever wording this method happened to default to.
+     *
      * @param allProfiles        every configured profile name
-     * @param configuredProfiles the subset of {@code allProfiles} that carry an exhausted pattern
+     * @param configuredProfiles the subset of {@code allProfiles} that carry the pattern
      */
-    public static String coverage(String patternKey, Set<String> allProfiles, Set<String> configuredProfiles) {
+    public static String coverage(String patternKey, UnsetMeaning unsetMeaning, Set<String> allProfiles,
+                                   Set<String> configuredProfiles) {
         if (configuredProfiles.isEmpty()) {
-            return "off (no profile has an " + patternKey + " configured; profiles: " + sorted(allProfiles) + ")";
+            return switch (unsetMeaning) {
+                case OFF -> "off (no profile has an " + patternKey + " configured; profiles: "
+                        + sorted(allProfiles) + ")";
+                case BUILT_IN_DEFAULT -> "built-in default for all profiles (no profile customises "
+                        + patternKey + "; profiles: " + sorted(allProfiles) + ")";
+            };
         }
         Set<String> unconfigured = new TreeSet<>(allProfiles);
         unconfigured.removeAll(configuredProfiles);

fleetd/src/test/java/dev/ltms/fleet/inject/CompletionResolverTest.java

@@ -20,6 +20,7 @@ import java.util.regex.Pattern;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /** Unit behaviour of the CB-106 completion resolver in isolation from the injector. */
@@ -884,19 +885,22 @@ class CompletionResolverTest {
     @Test
     void coverageIsOffWhenNoProfileHasAPatternConfigured() {
         assertEquals("off (no profile has an exhaustedPattern configured; profiles: [terra])",
-                CompletionResolver.coverage("exhaustedPattern", Set.of("terra"), Set.of()));
+                CompletionResolver.coverage("exhaustedPattern", CompletionResolver.UnsetMeaning.OFF,
+                        Set.of("terra"), Set.of()));
     }
 
     @Test
     void coverageIsFullWhenEveryProfileHasAPatternConfigured() {
         assertEquals("full (all profiles configured: [gx10, terra])",
-                CompletionResolver.coverage("exhaustedPattern", Set.of("terra", "gx10"), Set.of("terra", "gx10")));
+                CompletionResolver.coverage("exhaustedPattern", CompletionResolver.UnsetMeaning.OFF,
+                        Set.of("terra", "gx10"), Set.of("terra", "gx10")));
     }
 
     @Test
     void coverageIsPartialAndNamesWhichProfilesAreConfigured() {
         assertEquals("partial (configured: [terra]; not configured: [gx10])",
-                CompletionResolver.coverage("exhaustedPattern", Set.of("terra", "gx10"), Set.of("terra")));
+                CompletionResolver.coverage("exhaustedPattern", CompletionResolver.UnsetMeaning.OFF,
+                        Set.of("terra", "gx10"), Set.of("terra")));
     }
 
     /**
@@ -910,11 +914,42 @@ class CompletionResolverTest {
      *
      * <p>Every earlier test here passed the exhaustion case only, so none of them could see it. This
      * one pins that the message names the key the caller actually meant.
+     *
+     * <p>fleetd#415: the expected wording changed here too. {@code errorPattern} has a built-in
+     * fallback ({@link CompletionResolver#BACKEND_ERROR}), so an empty {@code configuredProfiles}
+     * for it is not "off" — see {@link #coverageDistinguishesOffFromBuiltInDefaultForTheSameEmptyInput}
+     * for the test built specifically to pin that distinction.
      */
     @Test
     void coverageNamesTheConfigKeyItsCallerMeansRatherThanAlwaysSayingExhaustedPattern() {
-        assertEquals("off (no profile has an errorPattern configured; profiles: [gx10, terra])",
-                CompletionResolver.coverage("errorPattern", Set.of("terra", "gx10"), Set.of()));
+        assertEquals("built-in default for all profiles (no profile customises errorPattern; "
+                        + "profiles: [gx10, terra])",
+                CompletionResolver.coverage("errorPattern", CompletionResolver.UnsetMeaning.BUILT_IN_DEFAULT,
+                        Set.of("terra", "gx10"), Set.of()));
+    }
+
+    /**
+     * fleetd#415: {@code coverage()} measures pattern coverage (how many profiles set the key), but
+     * for {@code errorPattern} the empty case is not the feature-off state — a profile with no
+     * configured {@code errorPattern} still runs the classification against
+     * {@link CompletionResolver#BACKEND_ERROR}. For {@code exhaustedPattern} there is no fallback,
+     * so empty really is off. Same shape of input (empty {@code configuredProfiles}, one profile),
+     * different {@link CompletionResolver.UnsetMeaning} — the wording must differ, or this method is
+     * back to conflating pattern coverage with feature state for the one key where they disagree.
+     */
+    @Test
+    void coverageDistinguishesOffFromBuiltInDefaultForTheSameEmptyInput() {
+        String exhaustedLine = CompletionResolver.coverage("exhaustedPattern",
+                CompletionResolver.UnsetMeaning.OFF, Set.of("gx10", "terra"), Set.of());
+        String errorLine = CompletionResolver.coverage("errorPattern",
+                CompletionResolver.UnsetMeaning.BUILT_IN_DEFAULT, Set.of("gx10", "terra"), Set.of());
+
+        assertEquals("off (no profile has an exhaustedPattern configured; profiles: [gx10, terra])",
+                exhaustedLine);
+        assertEquals("built-in default for all profiles (no profile customises errorPattern; "
+                        + "profiles: [gx10, terra])", errorLine);
+        assertNotEquals(exhaustedLine, errorLine,
+                "the same empty-coverage input must not read as the same feature state for both keys");
     }
 
     // --- fleetd#201 Unit 1: target-keyed backend-error pattern + typed sink ----------------------