feat(issue): add solution endpoint with auto-increment ID

- Add `ccw issue solution <id> --data '{...}'` for solution creation
- Add createSolution() with proper JSONL handling (trailing newline)
- Fix writeSolutions() to always add trailing newline
- Update plan.md to use CLI endpoint

Supports multiple solutions per issue with sequential IDs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude/commands/issue/plan.md

@@ -176,13 +176,22 @@ ${issueList}
 4. Plan solution with tasks (see issue-plan-agent.md for details)
 5. Write solutions to JSONL, bind if single solution
 
-### Generate Files
-\`.workflow/issues/solutions/{issue-id}.jsonl\` - Solution with tasks (schema: cat .claude/workflows/cli-templates/schemas/solution-schema.json)
+### Solution Creation (via CLI endpoint)
+```bash
+ccw issue solution <issue-id> --data '{"description":"...", "approach":"...", "tasks":[...]}'
+```
 
-**Solution ID Format**: \`SOL-{issue-id}-{seq}\` (e.g., \`SOL-GH-123-1\`, \`SOL-ISS-20251229-1\`)
+**CLI Endpoint Features:**
+| Feature | Description |
+|---------|-------------|
+| Auto-increment ID | `SOL-{issue-id}-{seq}` (e.g., `SOL-GH-123-1`) |
+| Multi-solution | Appends to existing JSONL, supports multiple per issue |
+| JSON output | Returns created solution with ID |
+
+**Schema Reference:** `cat .claude/workflows/cli-templates/schemas/solution-schema.json`
 
 ### Binding Rules
-- **Single solution**: Auto-bind via \`ccw issue bind <id> --solution <file>\`
+- **Single solution**: Auto-bind via `ccw issue bind <issue-id> <solution-id>`
 - **Multiple solutions**: Register only, return for user selection
 
 ### Return Summary

ccw/src/commands/issue.ts

@@ -333,7 +333,9 @@ function readSolutions(issueId: string): Solution[] {
 function writeSolutions(issueId: string, solutions: Solution[]): void {
   const dir = join(getIssuesDir(), 'solutions');
   if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
-  writeFileSync(getSolutionsPath(issueId), solutions.map(s => JSON.stringify(s)).join('\n'), 'utf-8');
+  // Always add trailing newline for proper JSONL format
+  const content = solutions.map(s => JSON.stringify(s)).join('\n');
+  writeFileSync(getSolutionsPath(issueId), content ? content + '\n' : '', 'utf-8');
 }
 
 function findSolution(issueId: string, solutionId: string): Solution | undefined {
@@ -363,6 +365,40 @@ function generateSolutionId(issueId: string, existingSolutions: Solution[] = [])
   return `SOL-${issueId}-${maxSeq + 1}`;
 }
 
+/**
+ * Create a new solution with proper JSONL handling
+ * Auto-generates ID if not provided
+ */
+function createSolution(issueId: string, data: Partial<Solution>): Solution {
+  const issue = findIssue(issueId);
+  if (!issue) {
+    throw new Error(`Issue "${issueId}" not found`);
+  }
+
+  const solutions = readSolutions(issueId);
+  const solutionId = data.id || generateSolutionId(issueId, solutions);
+
+  if (solutions.some(s => s.id === solutionId)) {
+    throw new Error(`Solution "${solutionId}" already exists`);
+  }
+
+  const newSolution: Solution = {
+    id: solutionId,
+    description: data.description || '',
+    approach: data.approach || '',
+    tasks: data.tasks || [],
+    exploration_context: data.exploration_context,
+    analysis: data.analysis,
+    score: data.score,
+    is_bound: false,
+    created_at: new Date().toISOString()
+  };
+
+  solutions.push(newSolution);
+  writeSolutions(issueId, solutions);
+  return newSolution;
+}
+
 // ============ Queue Management (Multi-Queue) ============
 
 function getQueuesDir(): string {
@@ -542,6 +578,34 @@ async function createAction(options: IssueOptions): Promise<void> {
   }
 }
 
+/**
+ * solution - Create solution from JSON data
+ * Usage: ccw issue solution <issue-id> --data '{"tasks":[...]}'
+ * Output: JSON with created solution (includes auto-generated ID)
+ */
+async function solutionAction(issueId: string | undefined, options: IssueOptions): Promise<void> {
+  if (!issueId) {
+    console.error(chalk.red('Issue ID required'));
+    console.error(chalk.gray('Usage: ccw issue solution <issue-id> --data \'{"tasks":[...]}\''));
+    process.exit(1);
+  }
+
+  if (!options.data) {
+    console.error(chalk.red('JSON data required'));
+    console.error(chalk.gray('Usage: ccw issue solution <issue-id> --data \'{"tasks":[...]}\''));
+    process.exit(1);
+  }
+
+  try {
+    const data = JSON.parse(options.data);
+    const solution = createSolution(issueId, data);
+    console.log(JSON.stringify(solution, null, 2));
+  } catch (err) {
+    console.error(chalk.red((err as Error).message));
+    process.exit(1);
+  }
+}
+
 /**
  * init - Initialize a new issue (manual ID)
  */
@@ -1639,6 +1703,9 @@ export async function issueCommand(
     case 'create':
       await createAction(options);
       break;
+    case 'solution':
+      await solutionAction(argsArray[0], options);
+      break;
     case 'init':
       await initAction(argsArray[0], options);
       break;