centaur: flight 8bd81239 R3 codex starter (scrybe#57 flowchart parser)

[hartsock]

Centaur-mode draft from drake-swarm flight `8bd81239` round 3

Single-candidate round (codex was the only worker that produced a diff). Arbiter trio voted Refine — the work isn't ship-quality per the arbiters, but it's enough scaffold for a human to iterate from. This PR makes that iteration loop concrete.

What's in

• `scrybe-mermaid-render/src/parser/flowchart.rs`: +286 / -14 — implements direction (`TD|LR|BT|RL`), minimal node + edge, label-bearing node, blank-line / comment skipping, error reporting for malformed shapes
• `scrybe-mermaid-render/src/parser/lexer.rs`: +9
• Built-in test module (#[cfg(test)]) with 7 tests covering directions, minimal edge, defaults

Closes #57 (when polished + arbiter-Pass'd).

Worker provenance

• Worker: codex (gpt-5-codex via codex-acp)
• Flight: 8bd81239 (round 3 of 3)
• Round_id: 1d86f6b7-3045-49f0-a17e-c0f63e165f98
• Arbiter outcome: Refine (3 replicas: drake-arbiter-{0,1,2}; quorum)

Why arbiters said Refine (inferred — not yet promoted from ndjson)

Arbiters consider the four `consider_criteria` from `.drake/swarm.toml`: compiles-cleanly, tests-added, style, structural-correctness. Likely flags on this round (review-side TODO):

• Verify shape primitives (rect / diamond / stadium / circle / rounded) — issue mermaid-render: parser(flowchart): all node shapes #58 scope, but referenced in flowchart.rs comments
• Edge variants beyond `-->` (per issue mermaid-render: parser(flowchart): edge variants #59)
• Subgraph blocks (per issue mermaid-render: parser(flowchart): subgraph blocks #60)
• Style helpers preserved or rejected

Centaur mode — how to land this

This is a draft. Pull the branch locally, run `cargo test -p scrybe-mermaid-render parser::flowchart`, iterate by hand on whatever arbiter notes you pull from the bare repo:

```bash
git fetch /mnt/agent-workspace/.drake-state/swarm-git/scrybe-mermaid-render.git \
'refs/heads/drake/flight/8bd81239/:refs/remotes/swarm/flight/8bd81239/'

compare codex's three rounds against each other for delta signal

git diff swarm/flight/8bd81239/rung/6906f4e4-/codex \
swarm/flight/8bd81239/rung/f5cd3257-/codex
```

The full arbiter per-replica notes live in the `drake-bake-off-verdicts` JetStream KV (NATS); the storyboard tab in drake-observatory will surface them inline once Phase 4 wiring lands.

Companion issues

• #1826 — `drake flight` CLI (would automate this push-as-PR step)
• #1827 — `capture_patch` base-ref bug (may have suppressed candidates this flight)
• Aviary Centaur UX (filing now — operator-driven iteration on a swarm-produced draft)

🤖 Centaur draft surfaced by drake-swarm; finishing it is a human task.