fix(office): stop duplicate addCharacter calls from starving the seat…

[adikeshri]

What & why

Working agents on the office floor stood wherever they happened to be —
doorways, next to furniture, on top of desk monitors — instead of walking to
and sitting at an empty desk. Every non-god agent was affected; only the
CEO/god agent ("Michael") reliably sat down.

Root cause: syncAgents() in OfficeFloor.tsx re-runs on every agents
array change, which includes the pty parser's per-chunk status/action writes
— i.e. very often while any agent is active. addCharacter() is async (it
awaits sprite frame loading) but had no guard against being re-invoked for
the same agent id before its first call finished registering in runtimes.

Each duplicate call:

• Claimed another seat from the finite seat pool via claimSeat().
• Spawned its own Character and added it to the scene.

Only the last call to finish ever landed in runtimes (the map key gets
overwritten); every earlier duplicate was silently orphaned — never added to
runtimes, so the per-frame ticker (for (const rt of runtimes.values()) rt.character.update(dt)) never advanced it again. It froze exactly wherever
it was, typically still at the entrance, mid walk-to-desk — which is why
agents appeared stuck in doorways and furniture instead of at an empty desk.
Once the seat pool was drained by duplicate claims, subsequently-added agents
fell back to the entrance tile as their "desk" entirely.

The god agent's seat claim is idempotent (if (agent.isGod) { seatClaims.add(GOD_SEAT); return GOD_SEAT; })
— every duplicate call resolves to the same desk — so the same race never
produced a visible symptom for it.

I independently ruled out a map/pathfinding data issue: parsed office.tmj's
collision layer and confirmed every named desk spawn point is BFS-reachable
from the entrance on the static walkability grid, and traced
Character.moveTo / walkToDeskAndSit — the walk-to-desk state machine is
correct once a Character is actually ticked. The defect is purely the
missing re-entrancy guard around addCharacter.

Fix: added a pendingAdds set so at most one addCharacter() call is
ever in flight per agent id, regardless of how often syncAgents fires
during the async getFrames() gap.

Closes #524

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Docs
• Build / CI

Evidence

Before

After

How I tested it

• OS: macOS (Darwin)
• Steps:
  1. Traced the syncAgents → addCharacter → runtimes control flow and
     confirmed there was no re-entrancy guard around the async gap.
  2. Parsed office.tmj's collision layer and ran BFS from the entrance to
     every named desk spawn point — all reachable — then traced
     Character.moveTo / walkToDeskAndSit to confirm the walk-to-desk
     state machine is correct once a Character is actually ticked.
  3. npm run typecheck — passes clean.
  4. npm run test:focused — 827/831 pass; the 4 failures are unrelated to
     this change (native node-pty/Electron binary not built in my
     environment) and don't touch OfficeFloor.tsx, Character.ts, or the
     seat-assignment path.
  5. npm run build — succeeds clean.

Credit (optional)

Discord:

X:

Checklist

• Before and after evidence is attached above, under both headings.
• npm run typecheck passes.
• npm run test:focused passes.
• npm run build succeeds.
• This PR is one change. Unrelated fixes belong in their own PR.
• I read the diff myself before opening this, and there is no debug
  output, commented-out code, or unrelated formatting churn in it.
• Any new UI derives from DESIGN.md / tokens.ts — no ad-hoc colors,
  spacing, or fonts.
• If I added art, it's my own or compatibly licensed, and listed in
  ATTRIBUTION.md.

[github-actions]

🚫 This PR is missing its before/after evidence

Every pull request here has to show its work. Screenshots or a short screen recording, before the change and after it.

• Before — no image or video under that heading
• After — no image or video under that heading

How to fix it: edit the description, keep the ### Before and ### After headings from the template, and drag an image or video under each. GitHub uploads it inline. This check re-runs the moment you save.

A bug fix with no visible surface still needs it: show the failing behaviour, then the same steps passing. A terminal recording is fine.

Genuinely nothing to show — a CI tweak, a typo, a dependency bump? A maintainer can apply the no-visual-change label. Please don't ask unless it truly has no observable effect.

📖 CONTRIBUTING.md → Evidence is mandatory