docs: 0.13.0 의 81.5% 주장을 정정하고, 살아남는 근거를 대신 적는다

CHANGELOG.md

@@ -4,7 +4,35 @@ All notable changes for the ContextGuard plugin are documented here.
 
 ## [Unreleased]
 
-_No unreleased changes._
+- **Corrected: the 81.5% figure below is wrong, and the fix that revealed it has
+  landed.** The 0.13.0 entry justifies making the Bash escrow the default with
+  "81.5% of new tokens per turn landing right after a Bash result". That table
+  had two defects. `last_result` was reset only per file, so a turn with no new
+  tool result inherited the previous turn's label; and the per-turn snapshot was
+  taken on every accepted row and cleared each time, while the usage reducer
+  selects the last row of a response group, so a multi-row response read an
+  already-cleared snapshot. Both are fixed. On the same kind of local corpus the
+  corrected table reads `no_tool_result` about 72% and Bash about 18%, and
+  `multi_result_turns` goes from roughly 108 to roughly 2,150. A local transcript
+  directory grows while you use it, so these are the shape of the correction
+  rather than fixed figures; the method is in `docs/safety-reference.md`.
+
+  **What the corrected table does and does not say about the escrow default.**
+  Turns divide on a second axis: whether the cached prefix was written or
+  extended. Among the incremental turns, where `cache_creation` grows roughly
+  with what just entered the context, Bash still ranks first at about 69%. That
+  is a ranking on one corpus, not a measured saving, and it is the narrower claim
+  the default now rests on.
+
+  The prefix-write turns are about 77% of `cache_creation`. Nothing that only
+  trims a single tool result changes those turns, because their size tracks the
+  whole context at that moment — though a hook that keeps the context smaller
+  over a session does reduce what a later rewrite has to write. The audit now
+  reports them as their own `cold_start` / `cache_rewrite` / `incremental`
+  fields.
+
+  Historical entries below keep the text they were published with; where an
+  affected figure appears, a pointer to this correction was added beside it.
 
 ## [0.14.0] - 2026-09-05
 
@@ -53,7 +81,8 @@ savings figure; the new audit sections exist so you can measure your own.
   command; in-budget output passes through untouched whether the command
   succeeded or failed. Local transcripts showed 81.5% of new tokens per turn
   landing right after a Bash result, so this is the surface the default now
-  covers. `--artifact-receipt` therefore means escrow-on-overflow; use
+  covers. (That figure was later found to be an artifact of two attribution
+  defects; see the correction under Unreleased.) `--artifact-receipt` therefore means escrow-on-overflow; use
   `--digest-always` to force a receipt for small output.
 - **Audit attributes new tokens to the preceding tool.** `new_tokens_per_turn`
   gains `by_preceding_tool` (which tool's result preceded each turn's

plugins/context-guard/skills/audit/SKILL.md

@@ -27,7 +27,7 @@ fi
 Report:
 
 - observed token buckets: input, output, cache_read, cache_creation;
-- new tokens per turn (cache_creation distribution) and the "by preceding tool_result" table: this is the quantity billed under prompt caching, so lead with the tool that precedes most of it;
+- new tokens per turn (cache_creation distribution) and the "by preceding tool_result" table: this is the quantity billed under prompt caching. The table covers every counted turn, so read the `cold_start` / `cache_rewrite` / `incremental` fields beside it before naming a tool. Turns that wrote the cached prefix track context size at that moment rather than what a tool just returned, so trimming one result does not change them. When those turns dominate, say so instead of naming the table's top tool;
 - model distribution;
 - query_source distribution: main, subagent, auxiliary;
 - top transcript files and commands observed;