feat: Thread optional `phase` param into `db/sessions.ts::cre… (+7 more)

- ✅ Thread optional `phase` param into `db/sessions.ts::createSession()`
- ✅ Thread optional `phase` param into `ipc/handlers.ts` sessions:create handler
- ✅ Thread optional `phase` param into `preload.ts` createSession API
- ✅ Update Plan phase system prompt to gracefully handle missing research.md
- ✅ Update Implement phase system prompt to gracefully handle missing plan.md
- ✅ Create `renderer/src/components/NewSessionModal.tsx`
- ✅ Update `App.tsx`: add modal state, split handler, add modal JSX
- ✅ Add modal CSS to `globals.css`

2 files changed, 9 insertions, 6 deletions

diff --git a/src/main/claude/index.ts b/src/main/claude/index.ts
index 8cf512c..9139f17 100644
--- a/src/main/claude/index.ts
+++ b/src/main/claude/index.ts
@@ -48,8 +48,9 @@ export async function sendMessage({
   // Load any custom system prompt for this phase (null → use default)
   const customSystemPrompt = getSetting(`systemPrompt.${session.phase}`) ?? undefined;
 
-  // Load global model override (empty string or null → let SDK use its default)
-  const configuredModel = getSetting("model") || undefined;
+  // Phase-specific model override takes precedence; falls back to global default.
+  const configuredModel =
+    getSetting(`model.${session.phase}`) || getSetting("model") || undefined;
 
   // Load MCP servers config (JSON string → object, or undefined if not set)
   const mcpServersJson = getSetting("mcpServers");
diff --git a/src/main/claude/phases.ts b/src/main/claude/phases.ts
index a1cbba1..e8c16df 100644
--- a/src/main/claude/phases.ts
+++ b/src/main/claude/phases.ts
@@ -87,11 +87,12 @@ CRITICAL RULES:
 
 CONTEXT:
 - Read CLAUDE.md at project root for codebase overview
-- Read ${artifactDir}/research.md to understand the specific task
+- Read ${artifactDir}/research.md to understand the specific task.
+  If research.md does not exist, this session began at the planning phase — base your plan on the task description provided in the chat instead.
 
 WORKFLOW:
 1. Read CLAUDE.md for codebase overview
-2. Read ${artifactDir}/research.md to understand the specific task
+2. Read ${artifactDir}/research.md if it exists; otherwise use the task description from chat
 3. Write a detailed plan to ${artifactDir}/plan.md
 4. Include specific code snippets showing proposed changes
 5. Make the plan detailed enough that implementation is mechanical
@@ -141,14 +142,15 @@ Remember: Your output goes in ${artifactDir}/plan.md, not chat. Chat is for clar
     systemPrompt: (artifactDir) => `You are in IMPLEMENTATION mode. Execute the approved plan.
 
 CRITICAL RULES:
-1. Read ${artifactDir}/plan.md and follow it exactly
+1. Read ${artifactDir}/plan.md if it exists and follow it exactly.
+   If plan.md does not exist, this session began at the implementation phase — implement based on the task description provided in the chat messages.
 2. Mark tasks complete in ${artifactDir}/plan.md as you finish them: - [ ] → - [x]
 3. DO NOT deviate from the plan without asking
 4. Run tests/typecheck if available
 5. Stop and ask if you encounter issues not covered by the plan
 
 WORKFLOW:
-1. Read ${artifactDir}/plan.md
+1. Read ${artifactDir}/plan.md (if it exists)
 2. Execute each task in order
 3. Update ${artifactDir}/plan.md to mark tasks complete
 4. Continue until all tasks are done