MassGen Experiment: Cherry Blossoms SVG

Multi-agent generation with Claude Code + Codex — March 31, 2026

Prompt

Generate cherry-blossoms.svg with two side-by-side scenes: left scene shows cherry blossoms at UW campus in Seattle with Drumheller Fountain, right scene shows cherry blossoms at a famous Tokyo temple. Use pink and white blossoms, detailed architecture, soft watercolor style. The SVG should be 1200x600px.

Agents

Agent 1 — Claude Code Winner
Model: claude-sonnet-4-6
Backend: claude_code
Rounds: 3 (generate, vote, final checkout)
Result: 629-line hand-authored SVG with watercolor filters, Gothic architecture, detailed fountain
Agent 2 — Codex Lost
Model: gpt-5.4
Backend: codex (native)
Rounds: 2 (generate, vote)
Result: Postcard-panel concept with Python generator, but 44 blossom elements had unresolved {x}, {y} template placeholders

Initial Outputs — Side by Side

Claude Code

CC SVG

Codex

Codex SVG

Coordination Timeline

E1 💭 CC starts streaming (no prior context)
E2 💭 Codex starts streaming (no prior context)
E3 ✨ CC submits answer agent1.1 — 629-line hand-authored SVG
E5 🔁 CC restart triggered → enters vote phase with context [agent1.1]
E7 🗳 CC votes for agent1.1 (own answer — only option at this point)
E8 ✨ Codex submits answer agent2.1 — postcard-panel SVG with Python generator
E10 🔁 Codex restart triggered → enters vote phase with context [agent1.1, agent2.1]
E12 🗳 CC votes for agent1.1 — "Agent2's SVG has 44 blossom elements with unresolved template placeholders"
E13 🗳 Codex votes for agent1.1 — "Verified both SVGs; agent2 has hundreds of unresolved placeholders rendering as black artifacts"
E14 🎯 CC selected as winner → produces final answer agent1.final

Vote Results

CC wins 2–0

Both agents voted for CC's output (agent1.1). The vote was unanimous.

CC's vote: "Agent1 has a complete, detailed 629-line SVG with proper architecture (Suzzallo Library Gothic facade, Drumheller Fountain with water jets, 5-story pagoda, torii gate), watercolor filters, and actual cherry blossom canopy elements. Agent2's SVG has a critical defect: all 44 blossom <use> elements contain literal template placeholders ({x}, {y}, {rot}, {scale}, {color}, {opacity}) that were never substituted with actual values."
Codex's vote: "Verified both SVGs from source and rendered output. Agent1's deliverable is a coherent, on-spec 1200x600 illustration with recognizable UW Drumheller Fountain and a Tokyo temple scene in the requested soft pink watercolor style. Agent2 has a nice postcard-panel concept, but its main SVG contains hundreds of unresolved template placeholders that render as obvious black artifact blobs."

Winner

Final Output — Claude Code (agent1.final)

Final SVG

Stats

2
Agents
6
Total Rounds
2–0
Vote (CC wins)
$4.95
Estimated Cost
3.8M
Input Tokens
102K
Output Tokens

Experiment Notes

Finding: --cwd-context rw and shadow workspaces

An earlier run (demo5) used --cwd-context rw, which creates massgen_shadow_* temp directories for file isolation. This caused Codex to write SVGs to the shadow dir instead of its assigned workspace, making them appear "missing" from logs. The ChangeApplier successfully copied files back to the project root, but the logs workspace snapshot didn't capture them.

This run (demo6) omitted --cwd-context rw, and both agents' SVGs were properly persisted in snapshots, workspaces, and logs.

Generated by Sutando using MassGen