[Feature] Centralize magic-number constants

[pathosDev]

Size / Priority

• Size: Trivial (~30+ sites consolidated)
• Category: C.2 Simplifications & DRY.
• Risk: low.

Affected files

• Across src/cluster/*, src/persistence/*, src/cache/* — magic-numbers scattered as inline literals.

Background

The codebase has ~30+ magic numbers as inline literals:

• 24 * 60 * 60 * 1000 (tombstone TTL).
• 5 * 60 * 1000 (default cleanup-tick interval).
• 1_000 (default gossip interval).
• 5_000 (default lock TTL, etc.).
• 30_000 (default ask timeout, etc.).
• 100 (default batch size).
• 1024 (frame size class, key-length cap, …).
• 16 * 1024 * 1024 (default wire-frame cap).

Inline literals:

• Make intent unclear at the call site.
• Are hard to search for systematically.
• Get accidentally divergent (one site says 60000, another says 60_000, another 1 * 60 * 1000).

Target code

Central constants file:

// src/util/Constants.ts (new) — or split by domain into:
// src/cluster/Constants.ts, src/persistence/Constants.ts, etc.

export const TOMBSTONE_TTL_MS = 24 * 60 * 60 * 1000;       // 24h
export const TOMBSTONE_PRUNE_INTERVAL_MS = 5 * 60 * 1000;    // 5min
export const DEFAULT_GOSSIP_INTERVAL_MS = 1_000;
export const DEFAULT_ASK_TIMEOUT_MS = 5_000;
export const DEFAULT_BATCH_SIZE = 100;
export const MAX_FRAME_BYTES = 16 * 1024 * 1024;             // 16 MB
export const MAX_PERSISTENCE_ID_LENGTH = 256;
// ... etc, organised by domain ...

Per-site usage:

// Before:
this.tombstoneTtlMs = settings.tombstoneTtlMs ?? 24 * 60 * 60 * 1_000;

// After:
this.tombstoneTtlMs = settings.tombstoneTtlMs ?? TOMBSTONE_TTL_MS;

Integration / risk

• No behavioural change.
• Cleaner code; easier to discover defaults.
• Allows future fork to override defaults centrally.

Test plan

1. Regression — all tests pass.
2. Documentation generation — central constants file shows all defaults at a glance.
3. Search: grep for Math\.|\d_\d|\d \* \d should find no remaining magic numbers.

Acceptance criteria

• Constants file(s) created.
• All identified sites migrated.
• Constants documented (JSDoc on each).
• Test suite passes.
• CHANGELOG entry: "All default constants now in src/util/Constants.ts (or domain-specific)".