Build the Godot menu port of Project Sylpheed, one milestone at a time.

## Your objective

`Syplheed-Reborn/docs/port/MISSION.md` — read it every iteration. It defines the
milestones (P0…P7 plus a gated S1), the gate each one must pass, and the two
decisions already made. Work the **lowest unfinished milestone**; do not skip
ahead because a later one looks more interesting.

Reverse engineering has not stopped, but it is no longer the goal. An RE item
earns attention when the port is blocked on it, and the write-up still goes in
`docs/re/` under the usual convention.

## Read these first, every iteration

Short on purpose, and the reason this prompt is short:

1. `docs/port/MISSION.md` — the objective, the milestones, what is out of scope.
2. `docs/port/FORMAT.md` — the export schema. It is **versioned**; changing it is
   a deliberate act with a version bump, not a silent edit.
3. `docs/re/REFUTED.md` — claims already tested and dead. Grep it for your nouns
   before designing anything.
4. `docs/re/METHOD.md` — the traps this corpus has already paid for.
5. `docs/re/INDEX.md` — what is already decoded. Re-deriving a ✅ row is not a
   finding.
6. `docker/agent/AGENT.md` — the container's tooling.

`docs/re/disc-atlas.html` is the map of how the assets reference each other —
useful when you need to find what feeds what.

**These files are the memory.** A finding that lives only in your context is lost
when the container dies.

## Each iteration

1. **Pick the lowest unfinished milestone** from MISSION.md. If you are mid-item,
   continue it rather than starting another.
2. **Build the smallest thing that reaches its gate.** The gate is an *artifact* —
   a validating JSON file, a screenshot, a human-clickable build — never "it
   compiles".
3. **Keep derived and authored apart.** `export/` is regenerated wholesale and is
   never hand-edited; `authored/` is hand-written and survives a re-export. If you
   are tempted to hand-fix a file under `export/`, the fix belongs in the exporter
   or in `authored/`. Every `authored/` entry carries a `why`.
4. **Write down what you learned** — in `docs/port/` for port decisions, in
   `docs/re/` for anything about the disc.
   * Refuted something → a line in `REFUTED.md`.
   * Bitten by a general trap → a line in `METHOD.md`.
   * Closed a format → update its `INDEX.md` row.
5. **Commit** to `auto/<topic>`, one logical change per commit.
6. **Publish**: `push-work`. Every iteration that produced a commit.
7. **Say plainly what you did not settle**, and stop.

## Hard rules

* **Never commit game assets.** `export/` is generated from the user's own disc
  and is gitignored. Code, schemas, authored mappings and docs only. If you are
  about to commit a sprite PNG or a transcoded video, stop.
* **No Rust in the Godot project, no GDExtension.** If Godot cannot read
  something, the exporter emits it differently. The wall between the two halves is
  the design, not an inconvenience.
* **Do not touch `crates/sylpheed-viewer`.** The Explorer is the human's
  verification tool, it is independent of the port, and it keeps its
  static-data-only rule. Do not refactor it to share code with the exporter.
* **Never commit to `main`**, never rebase a shared branch, never delete a branch,
  never rewrite history.
* **Do not touch another agent's worktree.** `git worktree list` first; branches
  marked `+` are checked out elsewhere.
* **One emulator at a time** — `run-canary` enforces it with a lockfile.
* **Measure the oracle; never infer it.** If you need to know what the real game
  does, run it. This applies with full force to the keyframe time unit and to any
  transition timing.
* **Do not improvise around a blocker.** If a milestone needs a decision only the
  user can make — a new dependency, a scope change, the Ready Room go/no-go —
  write what you found, note it in MISSION.md, and move to the next thing you can
  actually finish.

## Verifying

* `build-reborn test` wires up `SYLPHEED_DISC`; without it the disc tests
  self-skip and a green run means almost nothing.
* `sylpheed-cli screen render` is the reference renderer. When Godot draws a
  screen, diff it against the CLI's composite of the same build — they should
  agree, and where they do not, one of them is wrong and you must say which.
* Godot runs headless in this container (`godot --headless`), and
  `screenshot` captures the windowed one under Xvfb.
* A regenerated artifact that comes out byte-identical is strong evidence a
  change was additive. When it does change, check that every diff line pairs.

## Publishing

`push-work` pushes the current branch to origin. It refuses anything that is not
`auto/*` and never force-pushes, so the consolidated line stays a human's
decision. Run it **every iteration that produced a commit** — not at the end of
some longer arc, which is exactly when a container dies.

If it reports no credentials, say so in your reply and continue working. Do not
improvise another route out: no remote rewrite, no credential helper of your own,
no alternate transport. A push that is blocked is a blocked push.

## Pacing

One milestone step plus its write-up is a good iteration; a marathon is not. Stop
with a clean commit, a push, and an honest list of what is still open.

An emulator session must fit inside ONE turn — a Stop hook kills xenia when the
turn ends — but sequential tool calls within a turn are fine.

The loop runs on a fixed interval set by the harness, so you do **not** need to
arm the next wakeup yourself. Spend that attention on the write-up instead.