v5.11.13 — openclaw port: data-integrity, perf & symlink hardening

OpenClaw port improvements, contributed by @danikdanik (PRs #62–#67) and hardened via the torture-room QA pass.

Fixes

• #62 Clamp negative / non-finite token counts at the parse boundary (cost-accuracy fix)
• #64 Bound in-memory per-session tracking against unclean session ends (memory-leak fix)

Security

• #65 Refuse to follow symlinks on checkpoint writes (O_NOFOLLOW, TOCTOU narrowing)
• Follow-up: completed O_NOFOLLOW coverage across checkpoint-policy.ts (persistState, appendCheckpointEvent) and consolidated the write helper into a shared fs-utils.ts

Performance

• #63 Stream the first user prompt instead of parsing the whole transcript
• #66 Read each session file once in extractCostlyPrompts
• #67 Memoize normalizeModelName

All changes verified: tsc clean, build artifacts reproducible, runtime smoke-tested.