neon-sprawl/docs/plans/NEO-56-implementation-plan.md

NEO-56 — Implementation plan

Story reference

Field	Value
Key	NEO-56
Title	E3.M3: item_created / transfer-failure telemetry hook sites
Linear	https://linear.app/neon-sprawl/issue/NEO-56/e3m3-item-created-transfer-failure-telemetry-hook-sites
Module	E3.M3 — ItemizationAndInventorySchema · Epic 3 Slice 1 (E3M3-07)
Branch	NEO-56-item-created-transfer-failure-telemetry-hooks
Precursors	NEO-54 — PlayerInventoryOperations (Done); NEO-55 — inventory GET/POST HTTP (Done)
Pattern	NEO-49 / NEO-40 — comment-only engine anchors; NEO-30 — deny event + reasonCode

Kickoff clarifications

Topic	Question	Agent recommendation	Answer
Hook anchor	Engine only vs engine + HTTP?	Engine only — PlayerInventoryOperations (NEO-49 single-anchor precedent; NEO-55 deferred hooks here).	User: engine only.
Deny event shape	Per-reason events vs single deny + reasonCode?	inventory_transfer_denied + reasonCode (NEO-30 ability_cast_denied; epic inventory_full maps to a reason code).	User: single deny + reasonCode.
item_created scope	Add success only vs add + remove?	Successful add only (TryAddStack → Applied).	User: add success only.
Runtime behavior	Comments-only vs dev ILogger?	Comments-only — TODO(E9.M1); no production logging.	User: comments-only.
Manual QA doc	docs/manual-qa/NEO-56.md?	Yes — NEO-49 verification pattern.	User: yes.

Goal, scope, and out-of-scope

Goal: Document and place comment-only hook sites on the server-authoritative inventory mutation path for future E9.M1 catalog events item_created (successful add) and inventory_transfer_denied (transfer failures with stable reasonCode). Align with Epic 3 Slice 1 telemetry vocabulary (epic_03 — Slice 1).

In scope (from Linear + E3M3-07):

• Hook placement in PlayerInventoryOperations (TryAddStack / TryRemoveStack) with TODO(E9.M1) comments.
• server/README.md inventory subsection + E3_M3 module hook note.
• docs/manual-qa/NEO-56.md — verify comments + no behavior/API change.

Out of scope (from Linear):

• Telemetry ingest, dashboards (E9.M1).
• ILogger / metrics / dev-only log lines.
• Duplicate hook comments in PlayerInventoryApi (HTTP calls engine; NEO-55 plan deferred hooks to NEO-56).
• item_created on successful remove (kickoff decision).
• StoreMissing hooks (not a transfer failure — HTTP maps to 404).

Acceptance criteria checklist

• Hook sites documented in code (PlayerInventoryOperations) with TODO(E9.M1).
• item_created on successful add; inventory_transfer_denied + reasonCode on rule denies (including early validation denies).
• server/README.md documents hook placement.
• Matches Epic 3 Slice 1 vocabulary (item_created, inventory_full / transfer failures via reasonCode).

Technical approach

1. Authoritative surface: PlayerInventoryOperations — all inventory add/remove rules and outcomes. Callers (PlayerInventoryApi POST, future gather/craft) funnel here; no duplicate markers at HTTP.

2. Hook site A — item_created: In TryAddStack, immediately before returning PlayerInventoryMutationKind.Applied (after successful TryMutateSnapshot with no denyReason):

   • Comment block names future E9.M1 event item_created.
   • TODO(E9.M1): catalog emit (NEO-49 / NEO-30 style).
   • Planned payload fields: playerId, itemId, quantity, optional mutationKind/source when Slice 2+ callers exist.
   • Not on TryRemoveStack success (kickoff).

3. Hook site B — inventory_transfer_denied: On every Denied return path in TryAddStack and TryRemoveStack:

   • Early Deny(...) (e.g. invalid_quantity, invalid_item before store write).
   • Post-mutation deny when denyReason is set (inventory_full, insufficient_quantity).
   • Single comment pattern: catalog event inventory_transfer_denied + reasonCode from PlayerInventoryReasonCodes (inventory_full, invalid_item, insufficient_quantity, invalid_quantity).
   • Epic Slice 1 inventory_full is the flagship transfer-failure code; others share the same deny event shape (NEO-30 precedent).

4. No hook on StoreMissing: Outcome is missing player/store — not an inventory transfer rule deny.

5. Cross-references (minimal):

   • One-line pointer in PlayerInventoryMutationOutcome.cs or PlayerInventoryReasonCodes.cs xml summary → hook sites in PlayerInventoryOperations.
   • server/README.md: extend Player inventory (NEO-54 store, NEO-55 HTTP) with NEO-56 telemetry hooks subsection (anchor file + event names).
   • E3_M3_ItemizationAndInventorySchema.md: NEO-56 landed line under Related implementation slices.
   • documentation_and_implementation_alignment.md: E3.M3 row cites NEO-56 hook sites (still no E9.M1 ingest).

6. Regression: Run dotnet test on server solution; existing PlayerInventoryOperationsTests / PlayerInventoryApiTests unchanged (comments-only).

Files to add

Path	Purpose
docs/manual-qa/NEO-56.md	Manual QA: verify hook comment blocks + no API/behavior change.

Files to modify

Path	Rationale
server/NeonSprawl.Server/Game/Items/PlayerInventoryOperations.cs	NEO-56: item_created on add Applied; inventory_transfer_denied on all Denied paths in add/remove.
server/NeonSprawl.Server/Game/Items/PlayerInventoryReasonCodes.cs	Cross-reference deny reasonCode values → transfer-denied hook anchor (no behavior change).
server/README.md	Document inventory telemetry hook placement (NEO-56).
docs/decomposition/modules/E3_M3_ItemizationAndInventorySchema.md	Implementation snapshot: NEO-56 telemetry hooks.
docs/decomposition/modules/documentation_and_implementation_alignment.md	E3.M3 row: NEO-56 hook sites.

Tests

Path	Change
None required	Comments-only; existing PlayerInventoryOperationsTests and PlayerInventoryApiTests cover add/remove/deny paths.

Manual verification: docs/manual-qa/NEO-56.md — confirm item_created and inventory_transfer_denied comments, TODO(E9.M1), payload field notes, no new log statements; dotnet test regression.

Open questions / risks

Question / risk	Agent recommendation	Status
Future gather/craft callers	Hooks stay in engine; callers pass source/mutationKind in E9.M1 payload when catalog exists — document in hook comments as optional fields.	adopted
HTTP request correlation	Defer requestId to E9.M1 / future sink; do not add API-layer hooks (kickoff: engine only).	adopted
Partial stack placement on add	NEO-54 all-or-nothing add — single item_created emit for full requested quantity on Applied.	adopted

None blocking.