## At a glance
```csharp
public override void GetProperties(IPropertyList list)
{
base.GetProperties(list);
// Accumulate any number of free-text lines. On dispose the block flushes via
// AddChunked, splitting across as many OPL properties as needed so none can
// overflow the legacy 2D client's per-property buffer (which would crash it).
using var block = list.TextBlock();
if (luck > 0)
{
block.Add($"Luck Bonus: +{luck}%"); // zero-alloc interpolation
}
block.Add("Cannot be repaired".AsSpan()); // plain text, no string allocation
// Already holding a '\n'-joined string? Skip the builder and chunk directly:
// list.AddChunked(description);
}
```
## What
Adds a safe path for emitting **variable-length, free-form (non-cliloc) tooltip text**:
- **`ObjectPropertyList.Add(ReadOnlySpan<char>)`** overloads — append raw text with no string allocation. Makes the old single-arg `Add(string)` redundant (a `string` binds to the span overload implicitly), so it's dropped.
- **`AddChunked(ReadOnlySpan<char>)`** on `IPropertyList` — splits newline-joined text at `\n` boundaries across as many passthrough-cliloc properties as needed, so no single property exceeds the cap.
- **`OplTextBlock`** (`ref struct`) + **`IPropertyList.TextBlock()`** — an ergonomic builder that accumulates `\n`-joined lines (with a zero-alloc interpolated `Add($"...")` overload) and flushes via `AddChunked` on dispose. Usage: `using var block = list.TextBlock();`.
- **`MaxArgumentLength` (504)** — per-property cap with a hard backstop that clamps + logs anything that slips through.
## Why
The legacy 2D client copies each OPL property's text into a fixed ~512-char (1024-byte) buffer. A single property longer than that smashes an adjacent world object's vtable on the client heap and crashes the client. `AddChunked`/`OplTextBlock` keep multi-line content safely under the cap instead of risking one oversized `Add`.
## Docs
- `dev-docs/property-lists.md` — new "Multi-Line Free Text" deep-dive section; corrected the stale `IPropertyList` listing.
- `dev-docs/claude-skills/modernuo-property-lists.md` — condensed pattern + anti-pattern.
## Tests
9 tests pass (`OplTextBlockTests`, `ObjectPropertyListSpanAddTests`): line joining, empty-line skipping, no-line no-op, zero-alloc interpolation, and long-content chunking staying under `MaxArgumentLength`. Full `UOContent` build is green, confirming dropping `Add(string)` breaks no call sites.
## Summary
Captures the durable learnings from the message-interpolation work (PRs #2434, #2436, #2437, #2438, #2440) as reference documentation. **Doc-only PR — no code changes.**
The original Phase 2 audit (PR #2435) was development scaffolding and was closed unmerged once Phase 3 consumed it. This PR replaces it with proper reference docs that future authors can consult.
## What's added
### `dev-docs/string-handling.md`
- Promote `RawInterpolatedStringHandler` from a one-line note to a proper section listing all APIs that accept it (messages, OPL, gumps, packets).
- Document the `:L` lowercase format specifier.
- New comprehensive **"Interpolation Anti-Patterns"** section covering 8 patterns with before/after examples — applies to any handler-aware API:
1. Ternary with interpolated branches
2. Switch expression with interpolated arms
3. Pre-built local typed as `string`
4. `.ToString()` (or any string-returning method) inside a hole
5. String concatenation inside a hole
6. `string.Format` feeding a handler-aware API
7. LINQ-built strings inside a hole
8. Pre-built concat var
### `dev-docs/networking-packets.md`
- Add **"Player-Facing Message APIs"** section listing `Mobile` / `Item` / `NetState` message methods with their handler overloads.
- Note the `IBroadcastFilter` pattern for new spatial-broadcast helpers.
### `dev-docs/property-lists.md`, `dev-docs/gump-system.md`
- Cross-reference the new anti-patterns section.
- Add explicit `.ToString()` inside holes warning to property-lists (it had no such guidance before).
### `dev-docs/claude-skills/`
- Mirror the same content (condensed) in `modernuo-string-handling.md`, `modernuo-networking.md`, `modernuo-property-lists.md`, `modernuo-gump-system.md`.
- Add audit rule #17 to `modernuo-code-audit.md` covering all 8 anti-patterns with severity WARNING, plus the `:L` format spec.
### `CLAUDE.md`
- Add audit rule #18 summarizing the interpolation anti-patterns + `:L`, pointing to `dev-docs/string-handling.md` for details.
## Why this matters
Before this PR there was no documentation explaining when an interpolated string call site silently allocates a string despite the receiving API providing a handler overload. The Phase 3 cleanup (PRs #2436/#2437/#2438) discovered ~28 such sites in the codebase; without these docs the same patterns would re-emerge. The new audit rule + CLAUDE.md entry will catch them at write time.
Summary
- Adds CLAUDE.md at repo root with 14 terse code audit rules (always loaded, low token cost)
- Adds pointer files for other AI tools: AGENTS.md (Codex), GEMINI.md, .github/COPILOT-INSTRUCTIONS.md (Copilot), .cursorrules (Cursor) — all redirect to CLAUDE.md as single source of truth
- Gitignores /.claude so personal AI config isn't distributed
- Moves Claude skills to dev-docs/claude-skills/ (opt-in, not auto-loaded)
- Adds 14 dev-docs covering codebase conventions
Code Audit Rules (in CLAUDE.md)
1. LINQ tiered rules (Tier 1 free, Tier 2 warm, Tier 3 forbidden)
2. No Console.WriteLine — use LogFactory.GetLogger()
3. No concurrency primitives in game code
4. No World.Mobiles/World.Items iteration
5. Clean up refs in OnDelete()/OnAfterDelete()
6. Cancel timers in OnDelete()/OnAfterDelete()
7. STArrayPool<T>.Shared not ArrayPool<T>.Shared
8. PooledRefList<T> not new List<T>() on hot paths
9. Serialization: partial class, [Constructible], no serialized TimerExecutionToken
10. No Task.Run/new Thread() in game code
11. Never assume era — ask which expansion
12. _camelCase fields, PascalCase properties/methods
13. No empty gumps — use DisplayTo() pattern
14. PropertyList string literals must be {} holes, cliloc-as-argument uses :#
