Route Copilot's fast tier to gpt-5.6-luna and unpin capable

GraphcodeKit/Sources/Domain/BackendCommand.swift

@@ -24,20 +24,23 @@ extension CLISessionBackendKind {
   ///
   /// Deliberately per-backend rather than one shared alias list: Claude Code takes short
   /// aliases that keep resolving to the current model in a class, whereas Copilot's
-  /// `--model` takes explicit versioned ids from a fixed set (read off `copilot --help`
-  /// at 0.0.410). Pointing the same string at both would silently fail on one of them.
+  /// `--model` takes explicit versioned ids from a fixed set (read off `copilot help
+  /// config` at 1.0.84). Pointing the same string at both would silently fail on one of
+  /// them.
   ///
   /// `.standard` returns nil everywhere — passing no flag lets the backend's own default
-  /// apply, which is different from asserting what we think it is.
+  /// apply, which is different from asserting what we think it is. Copilot's `.capable`
+  /// is nil too: its list turns over fast enough that the pinned id (`claude-opus-4.6`)
+  /// had already gone by 1.0.84, and a capable loop that fails to launch is worse than
+  /// one on Copilot's own default.
   public func modelArguments(for tier: ModelTier) -> [String] {
     switch self {
     case .claudeCode:
       return tier.modelAlias.map { ["--model", $0] } ?? []
     case .copilotCLI:
       switch tier {
-      case .fast: return ["--model", "claude-haiku-4.5"]
-      case .standard: return []
-      case .capable: return ["--model", "claude-opus-4.6"]
+      case .fast: return ["--model", "gpt-5.6-luna"]
+      case .standard, .capable: return []
       }
     case .codex:
       // `-m` is real, but the valid model ids are not visible from `codex --help` and a

GraphcodeKit/Sources/Sessions/SummaryModelWriter.swift

@@ -65,7 +65,7 @@ public enum SummaryModelWriter {
   /// **The model argument comes from the backend, not from the tier.** `ModelTier`'s alias
   /// is Claude Code's spelling — `haiku` — and this passed it to all three, which is the
   /// exact mistake `BackendCommand.modelArguments(for:)` was written to prevent: Copilot's
-  /// `--model` takes explicit versioned ids (`claude-haiku-4.5`) and Codex's valid ids
+  /// `--model` takes explicit versioned ids (`gpt-5.6-luna`) and Codex's valid ids
   /// aren't visible from its `--help` at all, so it is given none and its own default
   /// applies. A wrong id fails at launch, which for this path means every rewrite quietly
   /// failing and the agent's own sentence standing — the feature would look switched off.

graphcode/Tests/CopilotBackendTests.swift

@@ -58,10 +58,10 @@ struct CopilotBackendTests {
     // at runtime, which is why the mapping is per-backend.
     #expect(
       CLISessionBackendKind.copilotCLI.modelArguments(for: .fast)
-        == ["--model", "claude-haiku-4.5"])
-    #expect(
-      CLISessionBackendKind.copilotCLI.modelArguments(for: .capable)
-        == ["--model", "claude-opus-4.6"])
+        == ["--model", "gpt-5.6-luna"])
+    // Capable is deliberately unpinned on Copilot: its id list turns over faster than a
+    // release cycle, and a launch that fails on a stale id is worse than the default.
+    #expect(CLISessionBackendKind.copilotCLI.modelArguments(for: .capable).isEmpty)
     // Claude Code's aliases stay aliases — they keep resolving to the current model.
     #expect(CLISessionBackendKind.claudeCode.modelArguments(for: .fast) == ["--model", "haiku"])
   }
@@ -76,10 +76,10 @@ struct CopilotBackendTests {
 
   @Test
   func aPinnedTierReachesTheCopilotArgv() {
-    let arguments = ZmxSessionLauncher.arguments(forNode: node(tier: .capable)) ?? []
+    let arguments = ZmxSessionLauncher.arguments(forNode: node(tier: .fast)) ?? []
 
     #expect(arguments.contains("--model"))
-    #expect(arguments.contains("claude-opus-4.6"))
+    #expect(arguments.contains("gpt-5.6-luna"))
   }
 
   @Test

graphcode/Tests/SummaryStoreTests.swift

@@ -214,7 +214,7 @@ struct SummaryStoreTests {
     // Copilot's `--model` takes an explicit versioned id, not Claude Code's short alias.
     #expect(
       SummaryModelWriter.invocation(forBackend: .copilotCLI, prompt: "p")
-        == ["copilot", "-p", "p", "--model", "claude-haiku-4.5"])
+        == ["copilot", "-p", "p", "--model", "gpt-5.6-luna"])
     // Codex's valid ids aren't visible from its `--help`, so it is given none and its own
     // default applies — an honest omission rather than a guessed id. Its non-interactive
     // mode is a subcommand.