fix: make mosaic init idempotent — detect existing config files

- mosaic-init bash script: detect existing SOUL.md/USER.md/TOOLS.md and
  prompt user to keep, import (re-use values as defaults), or overwrite.
  Non-interactive mode exits cleanly unless --force is passed.
  Overwrite creates timestamped backups before replacing files.

- launch.ts checkSoul(): prefer 'mosaic wizard' over legacy bash script
  when SOUL.md is missing, with fallback to mosaic-init.

- detect-install.ts: pre-populate wizard state with existing values when
  user chooses 'reconfigure', so they see current settings as defaults.

- soul-setup.ts: show existing agent name and communication style as
  defaults during reconfiguration.

- Added tests for reconfigure pre-population and reset non-population.

packages/mosaic/src/stages/detect-install.ts

@@ -87,7 +87,9 @@ export async function detectInstallStage(
     ],
   });
 
-  if (state.installAction === 'keep') {
+  if (state.installAction === 'keep' || state.installAction === 'reconfigure') {
+    // Load existing values — for 'keep' they're final, for 'reconfigure'
+    // they become pre-populated defaults so the user can tweak them.
     state.soul = await config.readSoul();
     state.user = await config.readUser();
     state.tools = await config.readTools();

packages/mosaic/src/stages/soul-setup.ts

@@ -24,6 +24,18 @@ export async function soulSetupStage(p: WizardPrompter, state: WizardState): Pro
         return undefined;
       },
     });
+  } else if (state.installAction === 'reconfigure') {
+    // Show existing value as default so the user can accept or change it
+    state.soul.agentName = await p.text({
+      message: 'What name should agents use?',
+      placeholder: state.soul.agentName,
+      defaultValue: state.soul.agentName,
+      validate: (v) => {
+        if (v.length === 0) return 'Name cannot be empty';
+        if (v.length > 50) return 'Name must be under 50 characters';
+        return undefined;
+      },
+    });
   }
 
   if (state.mode === 'advanced') {
@@ -38,7 +50,7 @@ export async function soulSetupStage(p: WizardPrompter, state: WizardState): Pro
     state.soul.roleDescription ??= DEFAULTS.roleDescription;
   }
 
-  if (!state.soul.communicationStyle) {
+  if (!state.soul.communicationStyle || state.installAction === 'reconfigure') {
     state.soul.communicationStyle = await p.select<CommunicationStyle>({
       message: 'Communication style',
       options: [
@@ -46,7 +58,7 @@ export async function soulSetupStage(p: WizardPrompter, state: WizardState): Pro
         { value: 'friendly', label: 'Friendly', hint: 'Warm but efficient, conversational' },
         { value: 'formal', label: 'Formal', hint: 'Professional, structured, thorough' },
       ],
-      initialValue: 'direct',
+      initialValue: state.soul.communicationStyle ?? 'direct',
     });
   }