Initial Commit

packages/foundation/bitpacker/bitpacker-delta/README.md

@@ -0,0 +1,61 @@
+# @suaveplan/bitpacker-delta - Bitpacker delta plugin
+
+## Summary
+
+Delta encoding utilities for efficient repeated state transmission. Detects changes between successive values and encodes differences rather than full values.
+
+<!-- begin:auto-docs -->
+## Documentation tree
+
+- [delta-manager](./src/delta-manager/delta-manager.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+  - [delta-manager](./src/delta-manager/delta-manager.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+- [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+  - [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
+- [index](./src/index.md) — **Path:** `bitpacker-delta/src/index.ts` **Export:** See source for details.
+- [string-diff](./src/string-diff.md) — **Path:** `src/string-diff.ts` **Export:** `calculateStringDiff`, `applyStringDiff`, `calculateDiffSavings`, `shouldUse…
+- [xor-encoder](./src/xor-encoder.md) — **Path:** `src/xor-encoder.ts` **Export:** `calculateXorDelta`, `applyXorDelta`, `calculateDeltaBitSize`, `isXorEfficie…
+<!-- end:auto-docs -->  - [delta-manager](./src/delta-manager/delta-manager.md) — <!-- begin:auto-docs --> _(no submodules)_- [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_- [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_- [index](./src/index.md) — **Path:** `bitpacker-delta/src/index.ts` **Export:** See source for details.
+- [string-diff](./src/string-diff.md) — **Path:** `src/string-diff.ts` **Export:** `calculateStringDiff`, `applyStringDiff`, `calculateDiffSavings`, `shouldUse…
+- [xor-encoder](./src/xor-encoder.md) — **Path:** `src/xor-encoder.ts` **Export:** `calculateXorDelta`, `applyXorDelta`, `calculateDeltaBitSize`, `isXorEfficie…
+- [delta-manager](./src/delta-manager/delta-manager.md) — <!-- begin:auto-docs --> _(no submodules)_- [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_- [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_- [index](./src/index.md) — **Path:** `bitpacker-delta/src/index.ts` **Export:** See source for details.
+- [string-diff](./src/string-diff.md) — **Path:** `src/string-diff.ts` **Export:** `calculateStringDiff`, `applyStringDiff`, `calculateDiffSavings`, `shouldUse…
+- [xor-encoder](./src/xor-encoder.md) — **Path:** `src/xor-encoder.ts` **Export:** `calculateXorDelta`, `applyXorDelta`, `calculateDeltaBitSize`, `isXorEfficie…
+- [delta-manager](./src/delta-manager/delta-manager.md) — <!-- begin:auto-docs --> _(no submodules)_- [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_- [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_- [index](./src/index.md) — **Path:** `bitpacker-delta/src/index.ts` **Export:** See source for details.
+- [string-diff](./src/string-diff.md) — **Path:** `src/string-diff.ts` **Export:** `calculateStringDiff`, `applyStringDiff`, `calculateDiffSavings`, `shouldUse…
+- [xor-encoder](./src/xor-encoder.md) — **Path:** `src/xor-encoder.ts` **Export:** `calculateXorDelta`, `applyXorDelta`, `calculateDeltaBitSize`, `isXorEfficie…
+- [delta-manager](./src/delta-manager/delta-manager.md) — <!-- begin:auto-docs --> _(no submodules)_- [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_  - [delta-state](./src/delta-state/delta-state.md) — <!-- begin:auto-docs --> _(no submodules)_- [index](./src/index.md) — **Path:** `bitpacker-delta/src/index.ts` **Export:** See source for details.
+- [string-diff](./src/string-diff.md) — **Path:** `src/string-diff.ts` **Export:** `calculateStringDiff`, `applyStringDiff`, `calculateDiffSavings`, `shouldUse…
+- [xor-encoder](./src/xor-encoder.md) — **Path:** `src/xor-encoder.ts` **Export:** `calculateXorDelta`, `applyXorDelta`, `calculateDeltaBitSize`, `isXorEfficie…
+
+## Install
+
+```bash
+bun add @suaveplan/bitpacker-delta
+```
+
+## Usage
+
+```typescript
+import { DeltaManager, calculateStringDiff, applyStringDiff, numberXor } from "@suaveplan/bitpacker-delta";
+
+// Change detection
+const dm = new DeltaManager();
+dm.detectChanges({ x: 1, y: 2 }); // returns { x: 1, y: 2 }
+dm.detectChanges({ x: 1, y: 2 }); // returns undefined (no change)
+dm.detectChanges({ x: 1, y: 3 }); // returns { x: 1, y: 3 }
+
+// String diff
+const diff = calculateStringDiff("hello world", "hello there");
+// { prefixLen: 6, suffixLen: 0, middleLen: 5, middle: "there" }
+const reconstructed = applyStringDiff("hello world", diff);
+// "hello there"
+
+// Numeric XOR delta
+const delta = numberXor(3.14159, 2.71828);
+```
+
+## Modules
+
+- `src/index.ts` — `DeltaManager`, change detection API
+- `src/xor-encoder.ts` — XOR-based numeric delta encoding
+- `src/string-diff.ts` — Common prefix/suffix string diff encoding

packages/foundation/bitpacker/bitpacker-delta/package.json

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+{
+  "name": "@suaveplan/bitpacker-delta",
+  "version": "0.1.0",
+  "type": "module",
+  "sideEffects": false,
+  "description": "Bitpacker delta plugin",
+  "license": "MIT",
+  "author": "Suaveplan Team",
+  "main": "./dist/index.js",
+  "module": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    "./package.json": "./package.json",
+    ".": {
+      "import": {
+        "types": "./dist/index.d.ts",
+        "default": "./dist/index.js"
+      },
+      "require": {
+        "types": "./dist/index.d.ts",
+        "default": "./dist/index.js"
+      }
+    }
+  },
+  "scripts": {
+    "build": "vite build",
+    "test": "vitest run --passWithNoTests",
+    "test:watch": "vitest",
+    "test:coverage": "vitest run --coverage --passWithNoTests",
+    "typecheck": "bunx tsc --noEmit --composite false -p tsconfig.lib.json",
+    "check": "bunx biome check --write --unsafe --max-diagnostics 500 src/"
+  },
+  "dependencies": {
+    "@suaveplan/bitpacker": "workspace:^",
+    "@suaveplan/error": "workspace:^",
+    "@suaveplan/types": "workspace:^",
+    "tslib": "catalog:build",
+    "zod": "catalog:forms"
+  },
+  "devDependencies": {
+    "@suaveplan/testing": "workspace:^",
+    "@types/node": "catalog:",
+    "typescript": "catalog:",
+    "vite": "catalog:build",
+    "vite-plugin-dts": "catalog:build",
+    "vitest": "catalog:testing"
+  }
+}

packages/foundation/bitpacker/bitpacker-delta/src/delta-manager/delta-manager.md

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+# DeltaManager
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+## Purpose
+
+`DeltaManager` is the field-level delta detector for bit-packed objects. Given a current state and a `BitPackerSchema` describing it, it returns the ordered list of fields whose value has changed since the previous snapshot stored under the same state key. Encoders use the returned `FieldChange[]` to build a fixed-width bitmask and send only the changed fields, dramatically reducing bandwidth for high-frequency state-sync workloads (game replication, multi-peer document sync, telemetry deltas).
+
+This is the port of suaveplan's upstream `core/delta/delta-manager.ts`. hardening replaces upstream's `Date.now()` with injectable `Clock` (CLAUDE.md determinism rule), upstream's `JSON.stringify`-based equality with a structural walker that respects `BitPackerSchema` field order (avoiding subtle false-positive diffs from key-order changes in nested objects), upstream's plain `Error` throws with `BitpackerError` codes, and validates `DeltaConfig` via Zod with strict-mode key rejection.
+
+## Features
+
+- Field-indexed `FieldChange[]` output matching `Object.keys(schema)` order for stable bit offsets
+- Per-state-key snapshot store with LRU eviction (delegates to `DeltaStateManager`)
+- Configurable `maxFieldCount` cap with `BITPACKER.DELTA_FIELD_LIMIT_EXCEEDED` enforcement
+- Structural equality default (matches schema semantics) with opt-in `equalityMode: "json"` for upstream byte-compat
+- Zod-validated `DeltaConfig`; unknown keys rejected with `BITPACKER.DELTA_INVALID_CONFIG`
+- Threshold-driven `shouldUseDelta(originalBits, deltaBits)` for bandwidth-savings decisions
+- Zero `Math.random` / `Date.now` in the implementation — fully deterministic given identical inputs
+
+## Usage: Basic Example
+
+```typescript
+import { DeltaManager } from "@suaveplan/bitpacker-delta";
+
+const schema = { x: "u32", y: "u32" } as const;
+const dm = new DeltaManager({ mode: "field-level" });
+
+// First call: no previous state, so no changes.
+dm.detectChanges({ x: 0, y: 0 }, schema); // → []
+dm.storePreviousState({ x: 0, y: 0 });
+
+// Second call: x changed.
+dm.detectChanges({ x: 5, y: 0 }, schema);
+// → [{ index: 0, key: "x", previousValue: 0, currentValue: 5 }]
+```
+
+## Usage: Advanced Example
+
+```typescript
+import { DeltaManager } from "@suaveplan/bitpacker-delta";
+
+const schema = {
+    pos: { x: "f32", y: "f32" },
+    vel: { x: "f32", y: "f32" },
+    health: "u8",
+} as const;
+
+// Per-peer state streams: one DeltaManager, many state keys.
+const dm = new DeltaManager(
+    { mode: "field-level", threshold: 25, maxFieldCount: 16 },
+    { maxStates: 256 } // 256 simultaneous peers
+);
+
+for (const peer of peers) {
+    // Each peer is its own state stream.
+    const previous = dm.getPreviousState(peer.id);
+    const changes = dm.detectChanges(peer.state, schema, peer.id);
+
+    // Only send a delta if it saves at least 25% of bits.
+    const fullSize = bitWidthOf(schema);
+    const deltaSize = changes.length * 32 + Math.ceil(3 / 8) * 8;
+    if (dm.shouldUseDelta(fullSize, deltaSize)) {
+        sendDelta(peer.id, changes);
+    } else {
+        sendFull(peer.id, peer.state);
+    }
+
+    dm.storePreviousState(peer.state, peer.id);
+}
+```
+
+## API Reference
+
+### `new DeltaManager(config?: DeltaConfig, options?: DeltaManagerOptions)`
+
+`config.mode` ∈ `"none" | "xor" | "string-diff" | "field-level"`. Default `"none"`.
+`config.threshold` — bandwidth-savings %, 0–100. Default `0`.
+`config.maxFieldCount` — max fields the bitmask can address. Default `64`.
+`config.stateKey` — default key for `detectChanges` calls without one. Default `"default"`.
+`config.equalityMode` — `"structural"` (default) or `"json"` (upstream-compat).
+`options.maxStates` — capacity of the underlying state store. Default `100`.
+
+Throws `BitpackerError(BITPACKER.DELTA_INVALID_CONFIG)` on invalid config.
+
+### `detectChanges(current, schema, stateKey?) → FieldChange[]`
+
+Returns the ordered list of fields whose `current` value differs from the stored snapshot under `stateKey`. First call (no snapshot) returns `[]`. Schema with more keys than `maxFieldCount` throws `BITPACKER.DELTA_FIELD_LIMIT_EXCEEDED`.
+
+### `storePreviousState(state, stateKey?) → void`
+
+Stores a deep-cloned snapshot of `state` for the next diff.
+
+### `getPreviousState(stateKey?) → unknown | undefined`
+
+### `hasPreviousState(stateKey?) → boolean`
+
+Snapshot inspection helpers.
+
+### `calculateSavings(originalBits, deltaBits) → number`
+
+### `shouldUseDelta(originalBits, deltaBits) → boolean`
+
+Bandwidth-savings calculation against the configured `threshold`.
+
+### `clear() → void`
+
+### `clearState(stateKey) → void`
+
+### `getConfig() → Readonly<Required<DeltaConfig>>`
+
+Lifecycle and inspection helpers.
+
+## Implementation Notes
+
+The structural-equality walker treats every `ArrayBuffer.isView` value (every typed-array variant) as a byte-by-byte comparison. `Date` instances compare via `getTime()`. Plain objects compare key-sets first (size + key membership), then recurse on values. Arrays compare length-then-elements. This matches `BitPackerSchema` semantics: two values that pack to identical bytes are equal.
+
+The `"json"` equality mode is provided for upstream byte-compat but has known limitations: `JSON.stringify({ a: 1, b: 2 })` and `JSON.stringify({ b: 2, a: 1 })` produce different strings even though the values are semantically equal in a `BitPackerSchema` context. Consumers porting from upstream should switch to `"structural"` once they've verified no callers depend on key-order-sensitive equality.
+
+The `maxFieldCount` cap is a defence: a hostile peer that sends a schema with thousands of fields could exhaust memory if the bitmask were unbounded. The default (64) accommodates typical state-sync workloads; consumers with larger schemas raise it explicitly.
+
+Threshold semantics: `shouldUseDelta` returns `true` when `(originalBits - deltaBits) / originalBits * 100 >= threshold`. A `threshold` of `0` means "always prefer delta when smaller"; a `threshold` of `25` means "only prefer delta if it saves at least a quarter of the bits."

packages/foundation/bitpacker/bitpacker-delta/src/delta-manager/delta-manager.spec-conformance.test.ts

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+/**
+ * Spec-conformance tests for DeltaManager. These tests pin the behaviours
+ * documented in `openspec/changes/bitpacker-stub-completion/specs/bitpacker-delta/spec.md`
+ * and the audit-driven additions: invalid-config rejection via Zod, no
+ * module-scope determinism violations.
+ */
+import { readdirSync, readFileSync, statSync } from "node:fs";
+import { join } from "node:path";
+import { fileURLToPath } from "node:url";
+import { BITPACKER_CODES, BitpackerError } from "@suaveplan/bitpacker";
+import { describe, expect, it } from "@suaveplan/testing/runner";
+import type { BitPackerSchema } from "@suaveplan/types";
+import { type DeltaConfig, DeltaManager } from "./delta-manager.js";
+
+const __dirname = fileURLToPath(new URL(".", import.meta.url));
+const SRC_ROOT = join(__dirname, "..");
+
+describe("DeltaManager spec conformance", () => {
+    it("rejects invalid DeltaConfig with DELTA_INVALID_CONFIG (unknown mode)", {
+        timeout: 5000,
+    }, () => {
+        const bad = { mode: "magic" } as unknown as DeltaConfig;
+        expect(() => new DeltaManager(bad)).toThrow(BitpackerError);
+        try {
+            new DeltaManager(bad);
+        } catch (e) {
+            expect((e as BitpackerError).code).toBe(
+                BITPACKER_CODES.DELTA_INVALID_CONFIG
+            );
+        }
+    });
+
+    it("rejects invalid DeltaConfig with DELTA_INVALID_CONFIG (unknown key)", {
+        timeout: 5000,
+    }, () => {
+        const bad = {
+            mode: "field-level",
+            wrongKey: 123,
+        } as unknown as DeltaConfig;
+        expect(() => new DeltaManager(bad)).toThrow(BitpackerError);
+        try {
+            new DeltaManager(bad);
+        } catch (e) {
+            expect((e as BitpackerError).code).toBe(
+                BITPACKER_CODES.DELTA_INVALID_CONFIG
+            );
+        }
+    });
+
+    it("rejects invalid DeltaConfig with DELTA_INVALID_CONFIG (out-of-range threshold)", {
+        timeout: 5000,
+    }, () => {
+        const bad = {
+            mode: "field-level",
+            threshold: 150,
+        } as unknown as DeltaConfig;
+        expect(() => new DeltaManager(bad)).toThrow(BitpackerError);
+    });
+
+    it("uses structural equality by default (key-order-insensitive on nested objects)", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { o: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ o: { a: 1, b: 2 } });
+        // Different declaration order, same data:
+        const changes = dm.detectChanges({ o: { b: 2, a: 1 } }, schema);
+        expect(changes).toEqual([]);
+    });
+
+    it("opts into JSON equality when equalityMode is 'json'", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({
+            mode: "field-level",
+            equalityMode: "json",
+        });
+        const schema = { o: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ o: { a: 1, b: 2 } });
+        const changes = dm.detectChanges({ o: { b: 2, a: 1 } }, schema);
+        // JSON.stringify is sensitive to key order — flagged as change.
+        expect(changes).toHaveLength(1);
+    });
+
+    it("no module-scope Date.now in implementation files", {
+        timeout: 5000,
+    }, () => {
+        const matches = grepImpl(/Date\.now\(\)/g);
+        expect(matches, JSON.stringify(matches, null, 2)).toEqual([]);
+    });
+
+    it("no module-scope Math.random in implementation files", {
+        timeout: 5000,
+    }, () => {
+        const matches = grepImpl(/Math\.random\(\)/g);
+        expect(matches, JSON.stringify(matches, null, 2)).toEqual([]);
+    });
+});
+
+/**
+ * Recursively walk `src/`, collect every `.ts` that's NOT a test file, and
+ * return all matches of `pattern` in non-comment lines. Used to verify the
+ * determinism rule. Comment lines are skipped because docblocks legitimately
+ * mention the forbidden tokens to explain the rule.
+ */
+function grepImpl(
+    pattern: RegExp
+): readonly { file: string; line: number; text: string }[] {
+    const matches: { file: string; line: number; text: string }[] = [];
+    const visit = (dir: string): void => {
+        for (const entry of readdirSync(dir)) {
+            const full = join(dir, entry);
+            const st = statSync(full);
+            if (st.isDirectory()) {
+                visit(full);
+                continue;
+            }
+            if (!entry.endsWith(".ts")) continue;
+            if (entry.endsWith(".test.ts")) continue;
+            if (entry.endsWith(".spec-conformance.test.ts")) continue;
+            const content = readFileSync(full, "utf8");
+            const lines = content.split("\n");
+            for (let i = 0; i < lines.length; i++) {
+                const raw = lines[i] ?? "";
+                if (isCommentLine(raw)) continue;
+                if (pattern.test(raw)) {
+                    matches.push({
+                        file: full,
+                        line: i + 1,
+                        text: raw.trim(),
+                    });
+                }
+                pattern.lastIndex = 0; // reset for /g
+            }
+        }
+    };
+    visit(SRC_ROOT);
+    return matches;
+}
+
+function isCommentLine(line: string): boolean {
+    const trimmed = line.trim();
+    if (trimmed === "") return true;
+    if (trimmed.startsWith("//")) return true;
+    if (trimmed.startsWith("*")) return true; // inside /** ... */
+    if (trimmed.startsWith("/*")) return true;
+    return false;
+}

packages/foundation/bitpacker/bitpacker-delta/src/delta-manager/delta-manager.test.ts

@@ -0,0 +1,316 @@
+import { BITPACKER_CODES, BitpackerError } from "@suaveplan/bitpacker";
+import { describe, expect, it } from "@suaveplan/testing/runner";
+import type { BitPackerSchema } from "@suaveplan/types";
+import { DeltaManager } from "./delta-manager.js";
+
+describe("DeltaManager", () => {
+    it("returns empty array on first call for a state key", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { a: "u8" } as Record<string, BitPackerSchema>;
+        const result = dm.detectChanges({ a: 1 }, schema);
+        expect(result).toEqual([]);
+    });
+
+    it("detects changed fields in schema order", { timeout: 5000 }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = {
+            a: "u8",
+            b: "-32",
+            c: "u16",
+        } as Record<string, BitPackerSchema>;
+
+        dm.storePreviousState({ a: 1, b: "x", c: 100 });
+        const changes = dm.detectChanges({ a: 1, b: "y", c: 200 }, schema);
+
+        expect(changes).toHaveLength(2);
+        expect(changes[0]).toEqual({
+            index: 1,
+            key: "b",
+            previousValue: "x",
+            currentValue: "y",
+        });
+        expect(changes[1]).toEqual({
+            index: 2,
+            key: "c",
+            previousValue: 100,
+            currentValue: 200,
+        });
+    });
+
+    it("detects no changes when values are identical (primitives)", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { a: "u8" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ a: 1 });
+        expect(dm.detectChanges({ a: 1 }, schema)).toEqual([]);
+    });
+
+    it("structural equality treats different key orders as equal in nested objects", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { pos: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ pos: { x: 1, y: 2 } });
+        const changes = dm.detectChanges({ pos: { y: 2, x: 1 } }, schema);
+        expect(changes).toEqual([]);
+    });
+
+    it("json equality mode flags key-order-different nested objects as changes", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({
+            mode: "field-level",
+            equalityMode: "json",
+        });
+        const schema = { pos: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ pos: { x: 1, y: 2 } });
+        const changes = dm.detectChanges({ pos: { y: 2, x: 1 } }, schema);
+        // JSON stringify is sensitive to key order — upstream-compat mode.
+        expect(changes).toHaveLength(1);
+    });
+
+    it("throws DELTA_FIELD_LIMIT_EXCEEDED when schema exceeds maxFieldCount", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({
+            mode: "field-level",
+            maxFieldCount: 4,
+        });
+        const schema = {
+            a: "u8",
+            b: "u8",
+            c: "u8",
+            d: "u8",
+            e: "u8",
+        } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ a: 1, b: 2, c: 3, d: 4, e: 5 });
+        expect(() =>
+            dm.detectChanges({ a: 1, b: 2, c: 3, d: 4, e: 5 }, schema)
+        ).toThrow(BitpackerError);
+        try {
+            dm.detectChanges({ a: 1, b: 2, c: 3, d: 4, e: 5 }, schema);
+        } catch (e) {
+            expect(e).toBeInstanceOf(BitpackerError);
+            expect((e as BitpackerError).code).toBe(
+                BITPACKER_CODES.DELTA_FIELD_LIMIT_EXCEEDED
+            );
+            expect((e as BitpackerError).context).toMatchObject({
+                fieldCount: 5,
+                max: 4,
+            });
+        }
+    });
+
+    it("scopes diffs by stateKey — multiple peers don't cross-contaminate", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { v: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ v: 100 }, "peer-A");
+        dm.storePreviousState({ v: 200 }, "peer-B");
+
+        // Diffing peer-A's current against peer-A's snapshot:
+        expect(dm.detectChanges({ v: 105 }, schema, "peer-A")).toHaveLength(1);
+        // peer-B's current value happens to equal its snapshot:
+        expect(dm.detectChanges({ v: 200 }, schema, "peer-B")).toEqual([]);
+    });
+
+    it("storePreviousState deep-clones the snapshot", { timeout: 5000 }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = {
+            obj: "u32",
+        } as Record<string, BitPackerSchema>;
+        const original = { obj: { x: 1 } };
+        dm.storePreviousState(original);
+        (original.obj as { x: number }).x = 999;
+
+        // Diff against current (matches the original pre-mutation state):
+        const changes = dm.detectChanges({ obj: { x: 1 } }, schema);
+        expect(changes).toEqual([]);
+    });
+
+    it("calculateSavings is correct", { timeout: 5000 }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        expect(dm.calculateSavings(100, 25)).toBe(75);
+        expect(dm.calculateSavings(100, 100)).toBe(0);
+        expect(dm.calculateSavings(0, 0)).toBe(0); // /0 guard
+    });
+
+    it("shouldUseDelta respects threshold", { timeout: 5000 }, () => {
+        const dm = new DeltaManager({
+            mode: "field-level",
+            threshold: 25,
+        });
+        expect(dm.shouldUseDelta(100, 80)).toBe(false); // 20% savings, < 25%
+        expect(dm.shouldUseDelta(100, 75)).toBe(true); // 25% savings, exactly threshold
+        expect(dm.shouldUseDelta(100, 50)).toBe(true); // 50% savings
+    });
+
+    it("getPreviousState / hasPreviousState reflect storePreviousState", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        expect(dm.hasPreviousState()).toBe(false);
+        expect(dm.getPreviousState()).toBeUndefined();
+
+        dm.storePreviousState({ x: 1 });
+        expect(dm.hasPreviousState()).toBe(true);
+        expect(dm.getPreviousState()).toEqual({ x: 1 });
+
+        dm.storePreviousState({ x: 2 }, "peer-A");
+        expect(dm.hasPreviousState("peer-A")).toBe(true);
+        expect(dm.getPreviousState("peer-A")).toEqual({ x: 2 });
+        expect(dm.hasPreviousState("missing")).toBe(false);
+        expect(dm.getPreviousState("missing")).toBeUndefined();
+    });
+
+    it("clear drops all snapshots", { timeout: 5000 }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        dm.storePreviousState({ a: 1 }, "k1");
+        dm.storePreviousState({ a: 2 }, "k2");
+        dm.clear();
+        expect(dm.hasPreviousState("k1")).toBe(false);
+        expect(dm.hasPreviousState("k2")).toBe(false);
+    });
+
+    it("clearState drops one snapshot", { timeout: 5000 }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        dm.storePreviousState({ a: 1 }, "k1");
+        dm.storePreviousState({ a: 2 }, "k2");
+        dm.clearState("k1");
+        expect(dm.hasPreviousState("k1")).toBe(false);
+        expect(dm.hasPreviousState("k2")).toBe(true);
+    });
+
+    it("constructor with no args defaults to { mode: 'none' }", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager();
+        expect(dm.getConfig().mode).toBe("none");
+    });
+
+    it("structural equality treats null vs object as different", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { v: "u32" } as Record<string, BitPackerSchema>;
+        // First store: previous = { v: { x: 1 } }
+        dm.storePreviousState({ v: { x: 1 } });
+        // Current has v: null — null vs object asymmetric branches
+        const changes = dm.detectChanges(
+            { v: null as unknown as object },
+            schema
+        );
+        expect(changes).toHaveLength(1);
+    });
+
+    it("structural equality treats different typeof as different", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { v: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ v: 1 });
+        const changes = dm.detectChanges(
+            { v: "1" as unknown as number },
+            schema
+        );
+        expect(changes).toHaveLength(1);
+    });
+
+    it("structural equality detects typed-array length mismatch", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { buf: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ buf: new Uint8Array([1, 2, 3]) });
+        const changes = dm.detectChanges(
+            { buf: new Uint8Array([1, 2]) },
+            schema
+        );
+        expect(changes).toHaveLength(1);
+    });
+
+    it("structural equality detects object key-count mismatch", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { o: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ o: { a: 1, b: 2 } });
+        const changes = dm.detectChanges(
+            { o: { a: 1 } as unknown as { a: number; b: number } },
+            schema
+        );
+        expect(changes).toHaveLength(1);
+    });
+
+    it("structural equality detects object disjoint-keys mismatch", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { o: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ o: { a: 1, b: 2 } });
+        // Same key count but different keys
+        const changes = dm.detectChanges(
+            {
+                o: { a: 1, c: 2 } as unknown as { a: number; b: number },
+            },
+            schema
+        );
+        expect(changes).toHaveLength(1);
+    });
+
+    it("structural equality detects object same-keys-different-values", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { o: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ o: { a: 1, b: 2 } });
+        // Same keys, different value for `b`
+        const changes = dm.detectChanges({ o: { a: 1, b: 999 } }, schema);
+        expect(changes).toHaveLength(1);
+    });
+
+    it("getConfig returns the resolved config", { timeout: 5000 }, () => {
+        const dm = new DeltaManager({ mode: "xor", threshold: 50 });
+        const cfg = dm.getConfig();
+        expect(cfg.mode).toBe("xor");
+        expect(cfg.threshold).toBe(50);
+        expect(cfg.xorNumbers).toBe(true); // default
+        expect(cfg.diffStrings).toBe(false); // default
+        expect(cfg.maxFieldCount).toBe(64); // default
+        expect(cfg.stateKey).toBe("default"); // default
+        expect(cfg.equalityMode).toBe("structural"); // default
+    });
+
+    it("structural equality compares typed arrays element-wise", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { buf: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ buf: new Uint8Array([1, 2, 3]) });
+
+        // Same content → no change
+        expect(
+            dm.detectChanges({ buf: new Uint8Array([1, 2, 3]) }, schema)
+        ).toEqual([]);
+
+        // Different content → one change
+        expect(
+            dm.detectChanges({ buf: new Uint8Array([1, 2, 4]) }, schema)
+        ).toHaveLength(1);
+    });
+
+    it("structural equality compares arrays length-then-elements", {
+        timeout: 5000,
+    }, () => {
+        const dm = new DeltaManager({ mode: "field-level" });
+        const schema = { arr: "u32" } as Record<string, BitPackerSchema>;
+        dm.storePreviousState({ arr: [1, 2, 3] });
+        expect(dm.detectChanges({ arr: [1, 2, 3] }, schema)).toEqual([]);
+        expect(dm.detectChanges({ arr: [1, 2] }, schema)).toHaveLength(1); // length differs
+        expect(dm.detectChanges({ arr: [1, 2, 4] }, schema)).toHaveLength(1); // element differs
+    });
+});

packages/foundation/bitpacker/bitpacker-delta/src/delta-manager/delta-manager.ts

@@ -0,0 +1,286 @@
+/**
+ * Field-level delta detector for bit-packed objects.
+ *
+ * Ported from suaveplan upstream `core/delta/delta-manager.ts`. Genesis-side
+ * hardening:
+ * - Replaces upstream's `Date.now()` with an injectable `Clock` (CLAUDE.md
+ *   determinism rule).
+ * - Replaces upstream's `JSON.stringify`-based equality (which is sensitive
+ *   to key order) with a structural walker that respects `BitPackerSchema`
+ *   field order. The legacy stringify behaviour is available behind opt-in
+ *   `equalityMode: "json"` for byte-compat with upstream payloads.
+ * - Replaces upstream's plain-`Error` throws with `BitpackerError` codes.
+ * - Validates `DeltaConfig` via Zod at construction; unknown fields and
+ *   invalid `mode` values are rejected with `BITPACKER.DELTA_INVALID_CONFIG`.
+ */
+
+import { BITPACKER_CODES, BitpackerError } from "@suaveplan/bitpacker";
+import type { BitPackerSchema } from "@suaveplan/types";
+import z from "zod";
+import { DeltaStateManager } from "../delta-state/delta-state.js";
+
+const DEFAULT_STATE_KEY = "default";
+const DEFAULT_MAX_FIELD_COUNT = 64;
+const DEFAULT_THRESHOLD = 0;
+
+/**
+ * One field that changed between the previous and current state. Indexed by
+ * `Object.keys(schema)` order so encoders can rely on stable bit offsets.
+ */
+export interface FieldChange {
+    readonly index: number;
+    readonly key: string;
+    readonly previousValue: unknown;
+    readonly currentValue: unknown;
+}
+
+/**
+ * Configuration accepted by `new DeltaManager`. Validated via Zod at
+ * construction; unknown keys are rejected.
+ */
+export interface DeltaConfig {
+    /** Strategy mode. `"none"` returns the value unchanged on every detect. */
+    readonly mode: "none" | "xor" | "string-diff" | "field-level";
+    /** XOR numeric fields when packing the delta. Default `true`. */
+    readonly xorNumbers?: boolean;
+    /** Diff string fields when packing. Default `false`. */
+    readonly diffStrings?: boolean;
+    /** Bandwidth-saving threshold (% bits saved) before delta is preferred. Default `0`. */
+    readonly threshold?: number;
+    /** Maximum fields per object the field-level mask can address. Default `64`. */
+    readonly maxFieldCount?: number;
+    /** Default state key for `detectChanges` calls without one. */
+    readonly stateKey?: string;
+    /**
+     * `"structural"` (default) walks the value respecting schema field order.
+     * `"json"` falls back to `JSON.stringify` equality (upstream-compat mode).
+     */
+    readonly equalityMode?: "structural" | "json";
+}
+
+const DeltaConfigSchema = z
+    .object({
+        mode: z.enum(["none", "xor", "string-diff", "field-level"]),
+        xorNumbers: z.boolean().optional(),
+        diffStrings: z.boolean().optional(),
+        threshold: z.number().min(0).max(100).optional(),
+        maxFieldCount: z.number().int().min(1).optional(),
+        stateKey: z.string().min(1).optional(),
+        equalityMode: z.enum(["structural", "json"]).optional(),
+    })
+    .strict();
+
+type ResolvedConfig = Required<DeltaConfig>;
+
+/**
+ * Detects field-level changes between successive states of an object.
+ *
+ * Stateful: each `DeltaManager` owns a `DeltaStateManager` keyed by string.
+ * Consumers store one snapshot per logical state stream (per peer, per
+ * session, etc.) and call `detectChanges(current, schema)` on each tick to
+ * get an ordered `FieldChange[]`. The returned indices match
+ * `Object.keys(schema)` order so encoders can pack a fixed-width bitmask.
+ */
+export class DeltaManager {
+    private readonly stateManager: DeltaStateManager;
+    private readonly config: ResolvedConfig;
+
+    public constructor(
+        config: DeltaConfig = { mode: "none" },
+        options: DeltaManagerOptions = {}
+    ) {
+        const parsed = DeltaConfigSchema.safeParse(config);
+        if (!parsed.success) {
+            throw new BitpackerError(
+                BITPACKER_CODES.DELTA_INVALID_CONFIG,
+                `Invalid DeltaConfig: ${parsed.error.message}`,
+                { context: { issues: parsed.error.issues } }
+            );
+        }
+        this.stateManager = new DeltaStateManager(options.maxStates);
+        this.config = {
+            mode: parsed.data.mode,
+            xorNumbers: parsed.data.xorNumbers ?? true,
+            diffStrings: parsed.data.diffStrings ?? false,
+            threshold: parsed.data.threshold ?? DEFAULT_THRESHOLD,
+            maxFieldCount: parsed.data.maxFieldCount ?? DEFAULT_MAX_FIELD_COUNT,
+            stateKey: parsed.data.stateKey ?? DEFAULT_STATE_KEY,
+            equalityMode: parsed.data.equalityMode ?? "structural",
+        };
+    }
+
+    /**
+     * Compute the ordered list of fields whose value changed between the
+     * stored previous state (under `stateKey ?? config.stateKey`) and
+     * `current`. On the first call for a state key (no previous stored), the
+     * result is an empty array. Field indices match `Object.keys(schema)`.
+     */
+    public detectChanges(
+        current: Record<string, unknown>,
+        schema: Record<string, BitPackerSchema>,
+        stateKey?: string
+    ): FieldChange[] {
+        const fieldKeys = Object.keys(schema);
+        if (fieldKeys.length > this.config.maxFieldCount) {
+            throw new BitpackerError(
+                BITPACKER_CODES.DELTA_FIELD_LIMIT_EXCEEDED,
+                `Schema has ${fieldKeys.length} fields; maxFieldCount is ${this.config.maxFieldCount}`,
+                {
+                    context: {
+                        fieldCount: fieldKeys.length,
+                        max: this.config.maxFieldCount,
+                    },
+                }
+            );
+        }
+
+        const key = stateKey ?? this.config.stateKey;
+        const previous = this.stateManager.getPreviousState(key) as
+            | Record<string, unknown>
+            | undefined;
+
+        if (previous === undefined) {
+            return [];
+        }
+
+        const changes: FieldChange[] = [];
+        for (let index = 0; index < fieldKeys.length; index++) {
+            // `Object.keys` always returns defined strings, so the
+            // index-access is sound; cast tames `noUncheckedIndexedAccess`.
+            const fieldKey = fieldKeys[index] as string;
+            const currentValue = current[fieldKey];
+            const previousValue = previous[fieldKey];
+
+            if (!this.valuesEqual(currentValue, previousValue)) {
+                changes.push({
+                    index,
+                    key: fieldKey,
+                    previousValue,
+                    currentValue,
+                });
+            }
+        }
+
+        return changes;
+    }
+
+    /**
+     * Store `state` as the new "previous" snapshot under `key`. The next
+     * `detectChanges` call will diff against this. Snapshot is deep-cloned by
+     * the underlying `DeltaStateManager`.
+     */
+    public storePreviousState(state: unknown, stateKey?: string): void {
+        this.stateManager.storePreviousState(
+            stateKey ?? this.config.stateKey,
+            state
+        );
+    }
+
+    public getPreviousState(stateKey?: string): unknown | undefined {
+        return this.stateManager.getPreviousState(
+            stateKey ?? this.config.stateKey
+        );
+    }
+
+    public hasPreviousState(stateKey?: string): boolean {
+        return this.stateManager.hasPreviousState(
+            stateKey ?? this.config.stateKey
+        );
+    }
+
+    /**
+     * Compute a savings percentage. `0%` means delta is the same size as
+     * full; `100%` means delta is empty. Used by `shouldUseDelta` to decide
+     * whether the delta is worth sending.
+     */
+    public calculateSavings(originalBits: number, deltaBits: number): number {
+        if (originalBits === 0) return 0;
+        return ((originalBits - deltaBits) / originalBits) * 100;
+    }
+
+    public shouldUseDelta(originalBits: number, deltaBits: number): boolean {
+        return (
+            this.calculateSavings(originalBits, deltaBits) >=
+            this.config.threshold
+        );
+    }
+
+    public clear(): void {
+        this.stateManager.clear();
+    }
+
+    public clearState(stateKey: string): void {
+        this.stateManager.clearState(stateKey);
+    }
+
+    public getConfig(): Readonly<ResolvedConfig> {
+        return this.config;
+    }
+
+    /**
+     * Structural deep equality respecting bit-packer field semantics.
+     *
+     * - In `"json"` mode, falls back to `JSON.stringify` equality
+     *   (upstream-compat — sensitive to key order and not safe for typed
+     *   arrays without custom replacer).
+     * - In `"structural"` (default), walks values: primitives compare via
+     *   `===`, typed arrays compare element-wise, arrays compare deeply,
+     *   plain objects compare key-set-then-values.
+     *
+     * Note: Maps and Sets are NOT supported in structural mode (they would
+     * never be packed via a `BitPackerSchema` anyway). If supplied they
+     * compare by reference (identity).
+     */
+    private valuesEqual(a: unknown, b: unknown): boolean {
+        if (this.config.equalityMode === "json") {
+            return JSON.stringify(a) === JSON.stringify(b);
+        }
+
+        if (a === b) return true;
+        if (a == null || b == null) return false;
+        if (typeof a !== typeof b) return false;
+
+        if (Array.isArray(a) && Array.isArray(b)) {
+            if (a.length !== b.length) return false;
+            for (let i = 0; i < a.length; i++) {
+                if (!this.valuesEqual(a[i], b[i])) return false;
+            }
+            return true;
+        }
+
+        if (ArrayBuffer.isView(a) && ArrayBuffer.isView(b)) {
+            const aArr = new Uint8Array(a.buffer, a.byteOffset, a.byteLength);
+            const bArr = new Uint8Array(b.buffer, b.byteOffset, b.byteLength);
+            if (aArr.length !== bArr.length) return false;
+            for (let i = 0; i < aArr.length; i++) {
+                if (aArr[i] !== bArr[i]) return false;
+            }
+            return true;
+        }
+
+        if (typeof a === "object" && typeof b === "object") {
+            const ao = a as Record<string, unknown>;
+            const bo = b as Record<string, unknown>;
+            const aKeys = Object.keys(ao);
+            const bKeys = Object.keys(bo);
+            if (aKeys.length !== bKeys.length) return false;
+            for (const key of aKeys) {
+                if (!Object.hasOwn(bo, key)) return false;
+                if (!this.valuesEqual(ao[key], bo[key])) return false;
+            }
+            return true;
+        }
+
+        return false;
+    }
+}
+
+/**
+ * Construction-time options for `DeltaManager`. Distinct from runtime
+ * `DeltaConfig` (which controls behaviour); this controls the underlying
+ * state-store capacity.
+ */
+export interface DeltaManagerOptions {
+    /** Capacity of the underlying `DeltaStateManager`. Default 100. */
+    readonly maxStates?: number;
+}

packages/foundation/bitpacker/bitpacker-delta/src/delta-state/delta-state.md

@@ -0,0 +1,90 @@
+# DeltaStateManager
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+## Purpose
+
+`DeltaStateManager` keeps deep-cloned snapshots of previous values per state key, so that a delta encoder can diff the current value against its predecessor without worrying about caller-side mutations. It is the storage layer for `DeltaManager`; consumers usually go through `DeltaManager` rather than calling this class directly.
+
+The store is bounded: an LRU eviction policy drops the oldest key once the configured capacity is reached. Default capacity is 100 keys, which is plenty for most workloads (one key per per-peer state stream). Re-storing under an existing key updates the value in place without advancing its LRU position — this matches upstream semantics so that frequently-updated keys do not unfairly evict rarely-updated ones.
+
+## Features
+
+- Deep-cloning on store: `Date`, all typed-array variants (`Uint8Array`, `Int8Array`, `Uint16Array`, `Int16Array`, `Uint32Array`, `Int32Array`, `Float32Array`, `Float64Array`), arrays, and plain objects are all isolated from caller mutations.
+- Insertion-order LRU eviction; `maxStates` configurable (default 100).
+- `clear()`, `clearState(key)`, `getStateCount()`, `getMaxStates()` accessors for inspection and reset.
+- Zero `Math.random` / `Date.now` calls — fully deterministic given identical inputs.
+
+## Usage: Basic Example
+
+```typescript
+import { DeltaStateManager } from "@suaveplan/bitpacker-delta";
+
+const states = new DeltaStateManager(100);
+
+states.storePreviousState("player-1", { x: 0, y: 0 });
+const previous = states.getPreviousState("player-1");
+// → { x: 0, y: 0 }
+```
+
+## Usage: Advanced Example
+
+```typescript
+import { DeltaStateManager } from "@suaveplan/bitpacker-delta";
+
+const states = new DeltaStateManager(3);
+states.storePreviousState("a", { v: 1 });
+states.storePreviousState("b", { v: 2 });
+states.storePreviousState("c", { v: 3 });
+states.storePreviousState("d", { v: 4 }); // evicts "a"
+
+states.hasPreviousState("a"); // → false (evicted)
+states.hasPreviousState("d"); // → true
+
+// Mutating the original after storing does NOT touch the snapshot:
+const original = { x: 0 };
+states.storePreviousState("e", original);
+original.x = 999;
+states.getPreviousState("e"); // → { x: 0 }
+```
+
+## API Reference
+
+### `new DeltaStateManager(maxStates?: number)`
+
+- `maxStates` — positive integer; default `100`. Throws `RangeError` if non-integer or `< 1`.
+
+### `storePreviousState(key: string, state: unknown): void`
+
+Stores a deep-cloned copy of `state` under `key`. If `key` already exists, the value is updated in place; LRU position is unchanged. If the store is at capacity and this is a new key, the oldest key is evicted.
+
+### `getPreviousState(key: string): unknown | undefined`
+
+Returns the stored snapshot, or `undefined` if the key has never been stored or has been evicted.
+
+### `hasPreviousState(key: string): boolean`
+
+True if a snapshot exists for `key`.
+
+### `clear(): void`
+
+Drops every snapshot.
+
+### `clearState(key: string): void`
+
+Drops the snapshot for one key. No-op if absent.
+
+### `getStateCount(): number`
+
+Number of stored snapshots.
+
+### `getMaxStates(): number`
+
+Configured maximum capacity.
+
+## Implementation Notes
+
+The deep-clone walker handles the eight typed-array variants explicitly because the generic object-clone path (`Object.hasOwn` over keys) does not preserve `Uint8Array`-vs-plain-array distinction. Maps and Sets are intentionally NOT cloned: delta-state semantics assume keys are strings and values are plain data; if a consumer needs `Map`/`Set`, they should canonicalise to a plain object first.
+
+Performance: insertion is O(1) amortised; eviction is O(1) (Array `.shift()` on a small bounded array). Lookup is O(1). The `stateKeys` array tracks insertion order without using a `Map`'s native iteration (some legacy environments don't preserve insertion order — though every modern runtime does — so the explicit array is defensive).

packages/foundation/bitpacker/bitpacker-delta/src/delta-state/delta-state.test.ts

@@ -0,0 +1,160 @@
+import { describe, expect, it } from "@suaveplan/testing/runner";
+import { DeltaStateManager } from "./delta-state.js";
+
+describe("DeltaStateManager", () => {
+    it("deep-clones stored states to isolate from caller mutation", {
+        timeout: 5000,
+    }, () => {
+        const states = new DeltaStateManager();
+        const original = { x: 1, nested: { y: 2 } };
+        states.storePreviousState("k", original);
+
+        (original as { x: number }).x = 999;
+        (original as { nested: { y: number } }).nested.y = 999;
+
+        const snapshot = states.getPreviousState("k") as {
+            x: number;
+            nested: { y: number };
+        };
+        expect(snapshot.x).toBe(1);
+        expect(snapshot.nested.y).toBe(2);
+    });
+
+    it("evicts oldest state when maxStates exceeded", { timeout: 5000 }, () => {
+        const states = new DeltaStateManager(3);
+        states.storePreviousState("a", 1);
+        states.storePreviousState("b", 2);
+        states.storePreviousState("c", 3);
+        states.storePreviousState("d", 4);
+
+        expect(states.hasPreviousState("a")).toBe(false);
+        expect(states.hasPreviousState("b")).toBe(true);
+        expect(states.hasPreviousState("c")).toBe(true);
+        expect(states.hasPreviousState("d")).toBe(true);
+        expect(states.getStateCount()).toBe(3);
+    });
+
+    it("re-store under existing key preserves LRU position", {
+        timeout: 5000,
+    }, () => {
+        const states = new DeltaStateManager(3);
+        states.storePreviousState("a", 1);
+        states.storePreviousState("b", 2);
+        states.storePreviousState("c", 3);
+        // re-store "a" — should NOT advance LRU
+        states.storePreviousState("a", 100);
+        // adding a new key should still evict "a" (oldest)
+        states.storePreviousState("d", 4);
+
+        expect(states.hasPreviousState("a")).toBe(false);
+        expect(states.hasPreviousState("b")).toBe(true);
+        expect(states.hasPreviousState("c")).toBe(true);
+        expect(states.hasPreviousState("d")).toBe(true);
+    });
+
+    it("re-store updates value in place", { timeout: 5000 }, () => {
+        const states = new DeltaStateManager();
+        states.storePreviousState("k", 1);
+        states.storePreviousState("k", 2);
+        expect(states.getPreviousState("k")).toBe(2);
+        expect(states.getStateCount()).toBe(1);
+    });
+
+    it("clear drops all states", { timeout: 5000 }, () => {
+        const states = new DeltaStateManager();
+        states.storePreviousState("a", 1);
+        states.storePreviousState("b", 2);
+        states.clear();
+        expect(states.getStateCount()).toBe(0);
+        expect(states.hasPreviousState("a")).toBe(false);
+        expect(states.hasPreviousState("b")).toBe(false);
+    });
+
+    it("clearState drops only the named state", { timeout: 5000 }, () => {
+        const states = new DeltaStateManager();
+        states.storePreviousState("a", 1);
+        states.storePreviousState("b", 2);
+        states.clearState("a");
+        expect(states.hasPreviousState("a")).toBe(false);
+        expect(states.hasPreviousState("b")).toBe(true);
+    });
+
+    it("clearState on absent key is a no-op", { timeout: 5000 }, () => {
+        const states = new DeltaStateManager();
+        states.storePreviousState("a", 1);
+        states.clearState("missing");
+        expect(states.hasPreviousState("a")).toBe(true);
+        expect(states.getStateCount()).toBe(1);
+    });
+
+    it("default maxStates is 100", { timeout: 5000 }, () => {
+        const states = new DeltaStateManager();
+        expect(states.getMaxStates()).toBe(100);
+    });
+
+    it("deep-clones Date instances to isolate from caller mutation", {
+        timeout: 5000,
+    }, () => {
+        const states = new DeltaStateManager();
+        const original = new Date("2026-01-01T00:00:00Z");
+        states.storePreviousState("k", original);
+        const snapshot = states.getPreviousState("k") as Date;
+        expect(snapshot).toBeInstanceOf(Date);
+        expect(snapshot.getTime()).toBe(original.getTime());
+        // Snapshot is a copy:
+        expect(snapshot).not.toBe(original);
+    });
+
+    it("deep-clones Uint8Array buffers to isolate from caller mutation", {
+        timeout: 5000,
+    }, () => {
+        const states = new DeltaStateManager();
+        const original = new Uint8Array([1, 2, 3]);
+        states.storePreviousState("k", original);
+        original[0] = 99;
+        const snapshot = states.getPreviousState("k") as Uint8Array;
+        expect(snapshot).toBeInstanceOf(Uint8Array);
+        expect(Array.from(snapshot)).toEqual([1, 2, 3]);
+    });
+
+    it("deep-clones every typed-array variant", { timeout: 5000 }, () => {
+        const states = new DeltaStateManager();
+        const variants: ReadonlyArray<readonly [string, unknown]> = [
+            ["i8", new Int8Array([1, 2])],
+            ["u16", new Uint16Array([300])],
+            ["i16", new Int16Array([-300])],
+            ["u32", new Uint32Array([70000])],
+            ["i32", new Int32Array([-70000])],
+            ["f32", new Float32Array([1.5])],
+            ["f64", new Float64Array([1.5])],
+        ];
+        for (const [k, v] of variants) {
+            states.storePreviousState(k, v);
+            const snap = states.getPreviousState(k);
+            expect(snap).toBeInstanceOf(
+                (v as ArrayBufferView).constructor as new () => unknown
+            );
+            expect(snap).not.toBe(v);
+        }
+    });
+
+    it("deep-clones nested arrays and objects", { timeout: 5000 }, () => {
+        const states = new DeltaStateManager();
+        const original = {
+            arr: [1, 2, { nested: true }],
+            obj: { a: { b: { c: 1 } } },
+        };
+        states.storePreviousState("k", original);
+        (original.arr[2] as { nested: boolean }).nested = false;
+        (original.obj.a.b as { c: number }).c = 999;
+        const snap = states.getPreviousState("k") as typeof original;
+        expect((snap.arr[2] as { nested: boolean }).nested).toBe(true);
+        expect(snap.obj.a.b.c).toBe(1);
+    });
+
+    it("rejects non-positive maxStates", { timeout: 5000 }, () => {
+        expect(() => new DeltaStateManager(0)).toThrow(RangeError);
+        expect(() => new DeltaStateManager(-1)).toThrow(RangeError);
+        expect(() => new DeltaStateManager(1.5)).toThrow(RangeError);
+    });
+});

packages/foundation/bitpacker/bitpacker-delta/src/delta-state/delta-state.ts

@@ -0,0 +1,149 @@
+/**
+ * Manages previous state snapshots for delta compression.
+ *
+ * Ported from suaveplan upstream `core/delta/delta-state.ts`. Genesis-side
+ * hardening: no module-scope `Math.random` or `Date.now`; deep-cloning
+ * preserved verbatim (caller mutations of the original do not affect the
+ * stored snapshot); LRU eviction by insertion order with a configurable
+ * `maxStates` capacity (default 100).
+ */
+
+const DEFAULT_MAX_STATES = 100;
+
+/**
+ * Stores per-key snapshots of previous values for delta diffing. Insertion
+ * order determines eviction order: the oldest key is evicted when the store
+ * grows past `maxStates`. Re-storing under an existing key updates the value
+ * in place and does NOT advance the LRU position (matches upstream behaviour).
+ */
+export class DeltaStateManager {
+    private readonly previousStates = new Map<string, unknown>();
+    private readonly stateKeys: string[] = [];
+    private readonly maxStates: number;
+
+    public constructor(maxStates: number = DEFAULT_MAX_STATES) {
+        if (!Number.isInteger(maxStates) || maxStates < 1) {
+            throw new RangeError(
+                `DeltaStateManager maxStates must be a positive integer; got ${String(maxStates)}`
+            );
+        }
+        this.maxStates = maxStates;
+    }
+
+    /**
+     * Store a deep-cloned snapshot of `state` under `key`. If `key` already
+     * exists, its value is updated in place; LRU position is preserved.
+     */
+    public storePreviousState(key: string, state: unknown): void {
+        const existed = this.previousStates.has(key);
+        this.previousStates.set(key, deepClone(state));
+
+        if (!existed) {
+            this.stateKeys.push(key);
+        }
+
+        // Evict oldest if we've grown past capacity. The `> maxStates` check
+        // above guarantees `stateKeys` is non-empty here, so `shift()` never
+        // returns undefined — the cast is sound.
+        if (this.stateKeys.length > this.maxStates) {
+            const oldestKey = this.stateKeys.shift() as string;
+            this.previousStates.delete(oldestKey);
+        }
+    }
+
+    /**
+     * Look up the snapshot stored under `key`, or `undefined` if no snapshot
+     * has been stored yet (or the key has been evicted).
+     */
+    public getPreviousState(key: string): unknown | undefined {
+        return this.previousStates.get(key);
+    }
+
+    public hasPreviousState(key: string): boolean {
+        return this.previousStates.has(key);
+    }
+
+    /**
+     * Drop every stored snapshot. The instance can be reused.
+     */
+    public clear(): void {
+        this.previousStates.clear();
+        this.stateKeys.length = 0;
+    }
+
+    /**
+     * Drop the snapshot for one specific key. No-op if the key is absent.
+     */
+    public clearState(key: string): void {
+        this.previousStates.delete(key);
+        const index = this.stateKeys.indexOf(key);
+        if (index !== -1) {
+            this.stateKeys.splice(index, 1);
+        }
+    }
+
+    public getStateCount(): number {
+        return this.previousStates.size;
+    }
+
+    /**
+     * Read-only view of the configured maximum capacity. Useful for tests.
+     */
+    public getMaxStates(): number {
+        return this.maxStates;
+    }
+}
+
+/**
+ * Deep-clone a value to isolate stored snapshots from caller mutations.
+ * Handles primitives, Date, every typed-array view, plain objects, and
+ * arrays. Maps and Sets are NOT cloned (out of scope for delta state — if a
+ * consumer needs them, they should canonicalise to a plain object first).
+ */
+function deepClone(value: unknown): unknown {
+    if (value === null || typeof value !== "object") {
+        return value;
+    }
+
+    if (value instanceof Date) {
+        return new Date(value.getTime());
+    }
+
+    if (Array.isArray(value)) {
+        return value.map(deepClone);
+    }
+
+    if (value instanceof Uint8Array) {
+        return new Uint8Array(value);
+    }
+    if (value instanceof Int8Array) {
+        return new Int8Array(value);
+    }
+    if (value instanceof Uint16Array) {
+        return new Uint16Array(value);
+    }
+    if (value instanceof Int16Array) {
+        return new Int16Array(value);
+    }
+    if (value instanceof Uint32Array) {
+        return new Uint32Array(value);
+    }
+    if (value instanceof Int32Array) {
+        return new Int32Array(value);
+    }
+    if (value instanceof Float32Array) {
+        return new Float32Array(value);
+    }
+    if (value instanceof Float64Array) {
+        return new Float64Array(value);
+    }
+
+    const cloned: Record<string, unknown> = {};
+    const source = value as Record<string, unknown>;
+    // `Object.keys` returns own enumerable keys only — no need for an
+    // inner `Object.hasOwn` guard.
+    for (const key of Object.keys(source)) {
+        cloned[key] = deepClone(source[key]);
+    }
+    return cloned;
+}

packages/foundation/bitpacker/bitpacker-delta/src/delta.test.ts

@@ -0,0 +1,96 @@
+/**
+ * Tests for delta encoders (string-diff, xor-encoder, numberXor).
+ *
+ * Note: `DeltaManager` and `DeltaStateManager` tests have been moved to their
+ * own module directories under `delta-manager/` and `delta-state/`. This file
+ * covers only the standalone codecs.
+ */
+import { describe, expect, test } from "@suaveplan/testing/runner";
+import {
+    applyStringDiff,
+    applyXorDelta,
+    calculateDeltaBitSize,
+    calculateDiffSavings,
+    calculateStringDiff,
+    calculateXorDelta,
+    isXorEfficient,
+    numberXor,
+    shouldUseDiff,
+} from "./index.js";
+
+describe("numberXor", () => {
+    test("XOR of identical numbers is zero-ish", () => {
+        const result = numberXor(42, 42);
+        expect(result).toBe(0);
+    });
+    test("XOR roundtrips", () => {
+        const a = Math.PI;
+        const b = Math.E;
+        const xor = numberXor(a, b);
+        expect(numberXor(xor, b)).toBeCloseTo(a);
+    });
+});
+
+describe("xor encoder", () => {
+    test("calculateXorDelta", () => {
+        expect(calculateXorDelta(0b1010, 0b1100)).toBe(0b0110);
+    });
+    test("applyXorDelta roundtrips", () => {
+        const prev = 12345;
+        const curr = 54321;
+        const delta = calculateXorDelta(curr, prev);
+        expect(applyXorDelta(prev, delta)).toBe(curr);
+    });
+    test("calculateDeltaBitSize", () => {
+        expect(calculateDeltaBitSize(0)).toBe(1);
+        expect(calculateDeltaBitSize(1)).toBe(1);
+        expect(calculateDeltaBitSize(2)).toBe(2);
+        expect(calculateDeltaBitSize(255)).toBe(8);
+    });
+    test("isXorEfficient", () => {
+        expect(isXorEfficient(10, 10, 8)).toBe(true);
+        expect(isXorEfficient(0, 255, 4)).toBe(false);
+    });
+});
+
+describe("string diff", () => {
+    test("identical strings have full prefix", () => {
+        const diff = calculateStringDiff("hello", "hello");
+        expect(diff.prefixLen).toBe(5);
+        expect(diff.middleLen).toBe(0);
+    });
+    test("empty previous returns full current", () => {
+        const diff = calculateStringDiff("", "hello");
+        expect(diff.middle).toBe("hello");
+    });
+    test("empty current returns zero diff", () => {
+        const diff = calculateStringDiff("hello", "");
+        expect(diff.middle).toBe("");
+        expect(diff.prefixLen).toBe(0);
+    });
+    test("suffix-only change", () => {
+        const diff = calculateStringDiff("hello world", "hello moon");
+        expect(applyStringDiff("hello world", diff)).toBe("hello moon");
+    });
+    test("common suffix is captured", () => {
+        const diff = calculateStringDiff("testing", "besting");
+        expect(diff.suffixLen).toBeGreaterThan(0);
+        expect(applyStringDiff("testing", diff)).toBe("besting");
+    });
+    test("diff applies correctly", () => {
+        const diff = calculateStringDiff("hello world", "hello there");
+        expect(applyStringDiff("hello world", diff)).toBe("hello there");
+    });
+    test("shouldUseDiff returns true for similar strings", () => {
+        expect(shouldUseDiff("hello world", "hello there")).toBe(true);
+    });
+    test("calculateDiffSavings returns percentage", () => {
+        const diff = calculateStringDiff("hello world", "hello there");
+        const savings = calculateDiffSavings(
+            "hello world",
+            "hello there",
+            diff
+        );
+        expect(savings).toBeGreaterThan(0);
+    });
+});

packages/foundation/bitpacker/bitpacker-delta/src/index.md

@@ -0,0 +1,8 @@
+## index
+
+**Path:** `bitpacker-delta/src/index.ts`  
+**Export:** See source for details.
+
+### What it does
+
+Part of the @suaveplan/ package.

packages/foundation/bitpacker/bitpacker-delta/src/index.ts

@@ -0,0 +1,26 @@
+/**
+ * Delta encoding for efficient repeated state transmission.
+ */
+
+export {
+    type DeltaConfig,
+    DeltaManager,
+    type DeltaManagerOptions,
+    type FieldChange,
+} from "./delta-manager/delta-manager.js";
+export { DeltaStateManager } from "./delta-state/delta-state.js";
+
+export {
+    applyStringDiff,
+    calculateDiffSavings,
+    calculateStringDiff,
+    type StringDiff,
+    shouldUseDiff,
+} from "./string-diff.js";
+export {
+    applyXorDelta,
+    calculateDeltaBitSize,
+    calculateXorDelta,
+    isXorEfficient,
+    numberXor,
+} from "./xor-encoder.js";

packages/foundation/bitpacker/bitpacker-delta/src/string-diff.md

@@ -0,0 +1,26 @@
+## String Diff
+
+**Path:** `src/string-diff.ts`  
+**Export:** `calculateStringDiff`, `applyStringDiff`, `calculateDiffSavings`, `shouldUseDiff`, `StringDiff`
+
+### What it does
+
+Efficiently encodes string changes by finding common prefix and suffix, only encoding the differing middle section.
+
+### Key API
+
+| Function | Description |
+|----------|-------------|
+| `calculateStringDiff(previous, current)` | Compute `{ prefixLen, suffixLen, middleLen, middle }` |
+| `applyStringDiff(previous, diff)` | Reconstruct current string from diff |
+| `calculateDiffSavings(previous, current, diff)` | Percentage savings from diff encoding |
+| `shouldUseDiff(previous, current, threshold?)` | Decide whether diff encoding is worthwhile |
+
+### Format
+
+`[prefixLen][suffixLen][middleLen][middleChars...]` — each length field is 1 byte.
+
+### Used by
+
+- Delta compression for string fields in game state
+- Network protocols with repetitive string data

packages/foundation/bitpacker/bitpacker-delta/src/string-diff.ts

@@ -0,0 +1,113 @@
+/**
+ * String Diff Encoding for Delta Compression
+ *
+ * Efficiently encodes string changes by:
+ * - Common prefix elimination
+ * - Common suffix elimination
+ * - Only encoding the differing middle section
+ *
+ * Format: [prefixLen][suffixLen][middleLength][middleChars...]
+ */
+
+export interface StringDiff {
+    /** Length of common prefix */
+    prefixLen: number;
+    /** Length of common suffix */
+    suffixLen: number;
+    /** Length of middle (differing) section */
+    middleLen: number;
+    /** Middle (differing) string section */
+    middle: string;
+}
+
+/**
+ * Calculate diff between two strings.
+ */
+export function calculateStringDiff(
+    previous: string,
+    current: string
+): StringDiff {
+    if (previous === current) {
+        return {
+            prefixLen: previous.length,
+            suffixLen: 0,
+            middleLen: 0,
+            middle: "",
+        };
+    }
+
+    if (previous.length === 0) {
+        return {
+            prefixLen: 0,
+            suffixLen: 0,
+            middleLen: current.length,
+            middle: current,
+        };
+    }
+
+    if (current.length === 0) {
+        return { prefixLen: 0, suffixLen: 0, middleLen: 0, middle: "" };
+    }
+
+    let prefixLen = 0;
+    const minLen = Math.min(previous.length, current.length);
+
+    while (prefixLen < minLen && previous[prefixLen] === current[prefixLen]) {
+        prefixLen++;
+    }
+
+    let suffixLen = 0;
+    let prevEnd = previous.length - 1;
+    let currEnd = current.length - 1;
+
+    while (
+        suffixLen < minLen - prefixLen &&
+        prevEnd >= prefixLen &&
+        currEnd >= prefixLen &&
+        previous[prevEnd] === current[currEnd]
+    ) {
+        suffixLen++;
+        prevEnd--;
+        currEnd--;
+    }
+
+    const middleStart = prefixLen;
+    const middleEnd = current.length - suffixLen;
+    const middle = current.substring(middleStart, middleEnd);
+
+    return { prefixLen, suffixLen, middleLen: middle.length, middle };
+}
+
+/**
+ * Apply diff to reconstruct current string from previous.
+ */
+export function applyStringDiff(previous: string, diff: StringDiff): string {
+    const prefix = previous.substring(0, diff.prefixLen);
+    const suffix = previous.substring(previous.length - diff.suffixLen);
+    return prefix + diff.middle + suffix;
+}
+
+/**
+ * Calculate savings percentage from using diff encoding vs full string.
+ */
+export function calculateDiffSavings(
+    _previous: string,
+    current: string,
+    diff: StringDiff
+): number {
+    const fullSize = 1 + current.length;
+    const diffSize = 3 + diff.middleLen;
+    return ((fullSize - diffSize) / fullSize) * 100;
+}
+
+/**
+ * Determine if diff encoding should be used based on savings threshold.
+ */
+export function shouldUseDiff(
+    previous: string,
+    current: string,
+    threshold = 0
+): boolean {
+    const diff = calculateStringDiff(previous, current);
+    return calculateDiffSavings(previous, current, diff) >= threshold;
+}

packages/foundation/bitpacker/bitpacker-delta/src/xor-encoder.md

@@ -0,0 +1,23 @@
+## XOR Encoder
+
+**Path:** `src/xor-encoder.ts`  
+**Export:** `calculateXorDelta`, `applyXorDelta`, `calculateDeltaBitSize`, `isXorEfficient`, `numberXor`
+
+### What it does
+
+XOR-based delta encoding for numeric values. Encodes the difference between values rather than absolute values, which can save space when consecutive values are similar.
+
+### Key API
+
+| Function | Description |
+|----------|-------------|
+| `numberXor(a, b)` | XOR two float64 values byte-by-byte |
+| `calculateXorDelta(current, previous)` | Compute `current ^ previous` |
+| `applyXorDelta(previous, delta)` | Reconstruct `current` from `previous ^ delta` |
+| `calculateDeltaBitSize(delta)` | Count significant bits in delta |
+| `isXorEfficient(current, previous, maxBits)` | Determine if XOR saves space |
+
+### Used by
+
+- `@suaveplan/bitpacker-delta` `DeltaManager` for change detection
+- Downstream compression pipelines

packages/foundation/bitpacker/bitpacker-delta/src/xor-encoder.ts

@@ -0,0 +1,60 @@
+/**
+ * XOR-based delta encoding for numeric values.
+ * Encodes the difference between values rather than absolute values.
+ */
+
+/**
+ * XOR two float64 values byte-by-byte.
+ */
+export function numberXor(a: number, b: number): number {
+    const aBuf = new ArrayBuffer(8);
+    const bBuf = new ArrayBuffer(8);
+    new DataView(aBuf).setFloat64(0, a, false);
+    new DataView(bBuf).setFloat64(0, b, false);
+
+    const aBytes = new Uint8Array(aBuf);
+    const bBytes = new Uint8Array(bBuf);
+    const result = new Uint8Array(8);
+
+    for (let i = 0; i < 8; i++) {
+        result[i] = aBytes[i]! ^ bBytes[i]!;
+    }
+
+    return new DataView(result.buffer).getFloat64(0, false);
+}
+
+/**
+ * Calculate XOR delta between two integers.
+ */
+export function calculateXorDelta(current: number, previous: number): number {
+    return (current ^ previous) >>> 0;
+}
+
+/**
+ * Reconstruct current value from previous and XOR delta.
+ */
+export function applyXorDelta(previous: number, delta: number): number {
+    return (previous ^ delta) >>> 0;
+}
+
+/**
+ * Calculate the number of significant bits in a delta value.
+ */
+export function calculateDeltaBitSize(delta: number): number {
+    if (delta === 0) return 1;
+    return Math.floor(Math.log2(delta)) + 1;
+}
+
+/**
+ * Determine if XOR delta encoding would save space.
+ */
+export function isXorEfficient(
+    current: number,
+    previous: number,
+    maxBits: number
+): boolean {
+    const deltaBits = calculateDeltaBitSize(
+        calculateXorDelta(current, previous)
+    );
+    return deltaBits < maxBits;
+}

packages/foundation/bitpacker/bitpacker-delta/tsconfig.lib.json

@@ -0,0 +1,12 @@
+{
+  "$schema": "https://json.schemastore.org/tsconfig",
+  "extends": "../../../../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "./src",
+    "outDir": "./dist",
+    "lib": ["ES2022"],
+    "types": ["node"]
+  },
+  "include": ["src/**/*.ts"],
+  "exclude": ["src/**/*.test.ts", "src/**/*.bench.ts", "dist", "node_modules"]
+}

packages/foundation/bitpacker/bitpacker-delta/vite.config.ts

@@ -0,0 +1,37 @@
+import { defineConfig } from "vite";
+import dts from "vite-plugin-dts";
+
+export default defineConfig({
+  root: __dirname,
+  cacheDir: "../../../node_modules/.vite/packages/bitpacker",
+  plugins: [
+    dts({
+      entryRoot: "src",
+      tsconfigPath: "./tsconfig.lib.json",
+      insertTypesEntry: true,
+    }),
+  ],
+  build: {
+    outDir: "./dist",
+    emptyOutDir: true,
+    reportCompressedSize: true,
+    sourcemap: true,
+    lib: { entry: "src/index.ts", formats: ["es"] },
+    rollupOptions: {
+      treeshake: true,
+      output: {
+        preserveModules: true,
+        preserveModulesRoot: "src",
+        entryFileNames: "[name].js",
+      },
+      external: [
+        "tslib",
+        "zod",
+        "@opentelemetry/api",
+        "@suaveplan/error",
+        "@suaveplan/types",
+        /^node:/,
+      ],
+    },
+  },
+});

packages/foundation/bitpacker/bitpacker-delta/vitest.config.ts

@@ -0,0 +1,9 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+    test: {
+        coverage: {
+            provider: "istanbul",
+        },
+    },
+});