docs: add Git workflow guidelines for agents and branch management

AGENTS.md

@@ -119,6 +119,26 @@ The living roadmap with per-version task checklists is in **[ROADMAP.md](ROADMAP
 - Finish each milestone's release checks **before** expanding scope. Cut map size and simulation complexity before compromising the core walking/driving experience.
 - Define the release checks in `Docs/release-checks.md`. If a check fails, do not tag the release; open a patch task in `ROADMAP.md` and report the failing check in `CHANGELOG.md`.
 
+## Git workflow
+
+Every agent works on a dedicated git branch. **Never commit work directly to `main`** (except the coordinator's integration merges).
+
+Before starting any task:
+
+1. **Scan `ROADMAP.md`** and pick a task — a level-three (`###`) section — to work on. Prefer sections that are already active (they may be yours) or open items in sections that are not owned by another agent. Check the active heading and assignment details to identify ownership.
+2. **Create a branch** for that task from the current `main`: `git checkout -b <topic>-<version>` (e.g. `git checkout -b facade-hero-0.1.4`). One branch per task; do not stack unrelated tasks on one branch.
+3. **Record the active branch in the heading** of the section you are working on in `ROADMAP.md`: append ` - active - <sessionId>` (and, if useful, the branch name) to the level-three heading. This is the only way other agents can see that work is in progress on this section.
+4. **Commit changes often** on that branch — small, focused commits with clear messages. Do not accumulate large uncommitted changes.
+5. **Push to remote when a checklist item is done** — each completed `- [x]` item in that section should be committed and pushed. This keeps the remote state visible and makes progress recoverable.
+6. When the section is complete, report the branch, changes, checks, and unresolved issues to the coordinator for integration (see *Parallel agent workflow* below). Do not merge into `main` yourself unless authorized.
+
+**Branch hygiene:**
+
+- Branch from the current `main` revision, not from a stale local checkout.
+- Keep `ROADMAP.md` checkbox updates on your branch — they are part of the work.
+- If a task needs a different camera angle, or affects visual review, follow the *Visual review* section before pushing.
+- If a task is abandoned, remove the ` - active - <sessionId>` suffix from the heading in `ROADMAP.md` and leave the branch for the coordinator to clean up.
+
 ## Parallel agent workflow
 
 - Designate one coordinator to serialize assignments, updates to the shared roadmap, and integration into `main`. Agree on task and file or asset ownership before work starts; avoid assigning the same section or binary asset to multiple agents at once.