v4.23.1 — Smaller session start, reachable tools

• SessionStart memory index trimmed by 57 % (2 990 -> 1 295 characters on
  the author's base, 30 -> 12 observations). Only guardrails, warnings and
  decisions; observations younger than 14 days first; automatic traces
  (chmod, restart…) excluded; Continuity and Tool Capture on one short line.
  Tunable: TS_SESSION_INDEX_MAX, TS_SESSION_INDEX_TYPES,
  TS_SESSION_INDEX_RECENT_DAYS, TS_SESSION_INDEX_EXCLUDE, TS_SESSION_LINE_MAX.
• move_symbol and checkpoint callable from ts_execute. The auto
  profile no longer lists them, and the sandbox allowlist did not have them
  either, so they had become unreachable. A test now checks that every tool
  dropped from the profile stays reachable through ts_execute.
• Benchmark variance. Three passes of the v4.23.0 measurement: cost
  -45 % ± 7 (range -39 % to -53 %), new tokens -59 % ± 6, wall time +40 %,
  Token Savior used in 23 sessions of 24. On 3 editing tasks (one pass) both
  arms succeed 3/3 with no measurable gain yet.
• Ops note: the index cache key includes EXCLUDE_EXTRA. Two processes sharing
  a project with different values (a daemon and a Claude Code session, say)
  invalidate each other's cache and rebuild the whole index on every switch.
  Give them the same value.