Bug: concurrent multi-provider submissions collide on idea ID and workspace

[laoliu5280]

Problem

When submitting the same idea with multiple providers in quick succession (e.g., --provider claude, --provider codex, --provider gemini), two bugs cause providers to run in the wrong workspace:

1. Idea ID collision (same-second submissions)

_generate_idea_id() in src/core/idea_manager.py:346 uses %Y%m%d_%H%M%S (1-second resolution) + md5(title)[:8]. Since the title hash is deterministic, two submissions of the same idea in the same second produce identical idea IDs, and the second YAML file overwrites the first.

Fix: Add randomness to the ID — e.g., append a short uuid4 hex or use microsecond precision (%f).

2. github_repo_name metadata overwrite

submit.py:160 writes metadata.github_repo_name to the idea YAML on each submission. When the same idea is submitted for multiple providers, each submit overwrites the previous provider's repo name. The runner (runner.py:176) then reads this single field and directs all providers to the last-submitted provider's workspace.

Fix: Store per-provider workspace info, e.g.:

metadata:
  workspaces:
    claude:
      github_repo_name: idea-slug-fd2b-claude
    codex:
      github_repo_name: idea-slug-318e-codex

Observed behavior

User submitted the same idea with providers claude, codex, and gemini within seconds. Claude ended up running inside the codex-named workspace (reasoning-trace-robustnes-318e-codex) because the codex submission overwrote the YAML metadata last.

Affected files

• src/core/idea_manager.py — _generate_idea_id()
• src/cli/submit.py — line 160, github_repo_name write
• src/core/runner.py — line 176, github_repo_name read