neon-sprawl/docs/plans/NEON-28-implementation-plan.md

# NEON-28 — Implementation plan

## Story reference

| Field | Value |
|--------|--------|
| **Key** | NEON-28 |
| **Title** | E1.M2: Camera integration hardening + dependent contract notes (per [decomposition backlog](../decomposition/modules/E1_M2_IsometricCameraController.md#jira-backlog)) |
| **Jira** | [NEON-28](https://neon-sprawl.atlassian.net/browse/NEON-28) |
| **Parent** | [NEON-1 — Epic 1 — Core Player Runtime](https://neon-sprawl.atlassian.net/browse/NEON-1) |
| **Module** | [E1.M2 — IsometricCameraController](../decomposition/modules/E1_M2_IsometricCameraController.md); umbrella [NEON-10](https://neon-sprawl.atlassian.net/browse/NEON-10) |

**Jira sync:** This plan was drafted from repo decomposition and code because the Atlassian MCP plugin is unavailable in this environment. **Reconcile the acceptance checklist below with the issue description in Jira** before merge; add or strike items so the plan matches Jira AC exactly.

**Board:** If the issue is still **To Do**, transition it to **In Progress** when implementation starts (Jira UI or MCP when available).

## Goal, scope, and out-of-scope

**Goal:** Close the E1.M2 “integration hardening” gap after follow + zoom + occlusion + pick-through shipped ([NEON-25](NEON-25-implementation-plan.md)–[NEON-27](NEON-27-implementation-plan.md), [NEON-30](NEON-30-implementation-plan.md)): make the camera stack **safe under edge cases** and write **explicit dependent contract notes** so downstream modules (notably **E6.M2 — ConsentAndRiskUxSignals**) know what they may rely on from the client camera layer.

**In scope**

- **Runtime hardening** on `IsometricFollowCamera`: occluder override bookkeeping must not **leak or fault** when occluder bodies are **freed**, removed from the tree, or otherwise invalid while still listed in `_occluder_overrides`; periodic reconciliation should **drop invalid keys** and **restore** mesh overrides where the `MeshInstance3D` is still valid.
- **Contract documentation (dependent notes):**
  - **E1.M2** module doc: short **“Consumer contract”** subsection — fields on `CameraState`, refresh cadence, meaning of `yaw` vs presentation yaw on the rig, client-only authority pointer to [client_server_authority.md](../decomposition/modules/client_server_authority.md#e1m2-isometriccameracontroller).
  - **E6.M2** module doc: **“E1.M2 camera adjacency”** subsection — what risk UX may read today (`CameraState` / rig path), explicit statement that **server must not** use camera pose for gameplay (link authority doc), and placeholder for future flags if product adds them.
- **Alignment hygiene:** Update [module_dependency_register.md](../decomposition/modules/module_dependency_register.md) **E1.M2 note** and [documentation_and_implementation_alignment.md](../decomposition/modules/documentation_and_implementation_alignment.md) **E1.M2** row to reflect NEON-28 completion (integration hardened + contracts noted).
- **Tests** for hardening paths that stay **headless-friendly** (no full `.tscn` required).

**Out of scope**

- **Yaw orbit** input, new zoom/occlusion techniques, or server-side camera awareness.
- **E9.M1** throttled telemetry (`camera_zoom_changed`, occlusion stress telemetry) — remains TODO on the rig / policy scripts.
- **E6.M2 implementation** (HUD, `RiskPrompt`, etc.) — documentation and stability only here.

## Acceptance criteria checklist

Confirm against Jira; edit this section if Jira differs.

- [ ] **Occluder lifecycle:** Fading an occluder then **queue_free** (or equivalent removal) does not leave permanent material overrides on surviving meshes and does not spam errors; `_occluder_overrides` does not retain invalid object keys.
- [ ] **Consumer contract documented:** E1.M2 documents **`CameraState`** semantics and cadence; E6.M2 documents what it may assume from E1.M2 today and points to authority rules.
- [ ] **Dependency / alignment docs** updated so E1.M2 no longer reads “integration hardening remains” for NEON-28’s scope (status/note row reflects shipped hardening + docs).
- [ ] **Automated tests** cover the new invalid-occluder / cleanup behavior (or document why impossible with current harness — prefer tests).

## Technical approach

1. **`isometric_follow_camera.gd`**
   - When iterating `_occluder_overrides` (restore pass and/or a small **sanity pass** each frame or only when keys change): if an occluder key **`not is_instance_valid(body)`**, **purge** the entry: for any stored `{mesh, surface, original}` rows, call `set_surface_override_material` only when `is_instance_valid(mi)`; then **erase** the dictionary key. This mirrors “restore then forget” without requiring the body to still exist.
   - Optionally run the same invalid-key purge at the **start** of `_update_occlusion` before computing `newly_blocking` to avoid freed keys participating in logic.
   - Keep behavior **identical** on the happy path (no extra allocations in the common case if implemented with a single backward pass over keys).

2. **Documentation**
   - **E1_M2_IsometricCameraController.md:** Add **NEON-28** bullet under implementation snapshot + **Consumer contract** (table or short list: `focus_world`, `distance`, `zoom_band_index`, `yaw` = orbit only, `follow_target_path`; refreshed every `_process` on the rig; presentation angle lives on rig exports, not duplicated in state unless we explicitly add a field later).
   - **E6_M2_ConsentAndRiskUxSignals.md:** Add **E1.M2 camera adjacency** — read `CameraState` from the follow rig when implementing risk UI; do not send camera pose to server for eligibility; link E1.M2 + authority.
   - **module_dependency_register.md** / **documentation_and_implementation_alignment.md:** Replace “hardening remains (NEON-28)” with **done** wording once this story merges.

3. **Tests**
   - Prefer a **GdUnit** suite that instantiates the camera script in isolation (or minimal scene) if needed: register a fake occluder flow is hard without physics — **fallback:** unit-test a **new static helper** e.g. `prune_invalid_occluder_entries(overrides: Dictionary) -> void` extracted for testability, or test via internal method if extraction is too heavy. **Minimal approach:** extract a small `static func` that takes the override dict and validates keys (document in plan — if we keep logic inline only, use a test scene with `StaticBody3D` + mesh under test project — only if CI can run it headless).

   **Decision during implementation:** Prefer **extracted static** `prune_freed_occluder_overrides(overrides: Dictionary) -> void` (or similar) that only uses `is_instance_valid` + restore loop so tests do not need `World3D`. Keeps `isometric_follow_camera.gd` as the single owner of restore semantics by having the static call the same restore logic via a callback — actually simpler: **instance method** `_purge_invalid_occluder_keys() -> void` called from `_update_occlusion` entry; test by subclassing or by scene-free test using `Engine.get_main_loop()` — hardest.

   **Pragmatic test path:** Add `isometric_follow_camera.gd` **static** `func occluder_override_key_is_valid(body: Variant) -> bool` returning `body is Node3D and is_instance_valid(body)` — test the static; implementation uses it when filtering keys. Low ceremony, proves the guard exists.

## Decisions

| Topic | Choice | Rationale |
|-------|--------|-----------|
| **API surface for E6.M2** | **Docs only** in NEON-28 | No new `CameraState` fields until a risk UX story needs them; avoids speculative schema. |
| **Invalid occluder handling** | **Purge + restore surviving meshes** | Prevents stuck transparency and dictionary leaks when level chunks or props despawn. |
| **Jira AC** | **Reconcile after fetch** | Decomposition title is the source for this draft; Jira remains canonical. |

## Files to add

**None** — changes land in existing `isometric_follow_camera.gd`, decomposition docs, and `client/test/isometric_follow_camera_test.gd`. If occlusion tests grow large during implementation, add `client/test/isometric_follow_camera_occlusion_hardening_test.gd` (listed as optional under [Tests](#tests)).

## Files to modify

| Path | Rationale |
|------|-----------|
| `client/scripts/isometric_follow_camera.gd` | Invalid occluder key purge + optional small static/helper for testability; keep happy-path behavior unchanged. |
| `docs/decomposition/modules/E1_M2_IsometricCameraController.md` | NEON-28 snapshot + consumer contract for `CameraState` / rig. |
| `docs/decomposition/modules/E6_M2_ConsentAndRiskUxSignals.md` | Dependent notes: E1.M2 adjacency + authority link. |
| `docs/decomposition/modules/module_dependency_register.md` | E1.M2 note: NEON-28 complete vs “remains.” |
| `docs/decomposition/modules/documentation_and_implementation_alignment.md` | E1.M2 row: reflect hardening + contract notes shipped. |

## Tests

| File | Coverage |
|------|----------|
| `client/test/isometric_follow_camera_test.gd` | **Change.** Add tests for any **new static guard** (e.g. invalid/freed `Node3D` key handling) or for **occluder override key validity** helper if introduced. |
| `client/test/isometric_follow_camera_occlusion_hardening_test.gd` | **Optional add.** Only if tests are too large for the existing suite; split occluder-lifecycle cases here. |

**Manual verification:** Run main scene; stand behind `Obstacle` to trigger fade; use debugger or a one-off dev step to free the obstacle node and confirm no errors and materials on other objects look correct. Repeat zoom in/out and click-through (NEON-30) smoke check.

## Open questions / risks

- **Jira AC drift:** Issue text may list extra items (e.g. specific perf or UX gates). Re-read NEON-28 in Jira when the plugin works and **update this plan** before implementation lands.
- **Headless tests vs freed `Object`:** Freed instance behavior in GDScript is subtle; prefer **static** tests on `Variant` / validity helpers plus one manual free-node check in editor.
- None otherwise.