goldstandard: destructive-prepend prohibition as knowledge law + PreToolUse hook

.claude/hooks/anti-pattern-matching.sh

@@ -21,20 +21,39 @@ tool="$(printf '%s' "$input" | jq -r '.tool_name // ""')"
 
 RULE='ANTI-MUSTER-REGEL (Operator-Direktive): Grep/grep/rg/sed/tail/head sind NUR schnelle Discovery-Suche ueber den kompletten Corpus (ein Symbol/eine Datei lokalisieren) — NIEMALS Ersatz fuers Verstehen. Auf einen Treffer NICHT handeln (editieren, loeschen, beurteilen, "verstanden" behaupten), bevor die betroffene Datei VOLLSTAENDIG mit dem Read-Tool gelesen wurde. Verstehen = ganzes Read, kein Snippet. (Grund: geloeschter Code, der nur gemustert, nie gelesen wurde.)'
 
+# Destructive-prepend guard (operator directive, 2026-08-30, after
+# open(p, "w").write(entry + open(p).read()) truncated PR_ARC_INVENTORY.md
+# 5876 -> 32 lines in #1081; restored #1082; law:
+# .claude/knowledge/never-truncate-a-file-you-still-need-to-read.md).
+# Non-blocking: injects the rule when a Bash command combines opening a file
+# for writing with reading in the same expression/pipeline.
+PREPEND_RULE='DESTRUCTIVE-PREPEND PROHIBITED (P0, locked 2026-08-30): never open a file for writing/truncation in the same expression or pipeline that still READS that file. open(p, "w") truncates BEFORE the argument open(p).read() runs (destroyed 5876 lines of PR_ARC_INVENTORY.md in #1081); "sort f > f" is the same defect. Prepend = read into a variable, compose in memory, THEN write — or use the Edit tool. Mandatory post-check after every ledger write: wc -l; an append-only file that got SHORTER is always a defect. Law: .claude/knowledge/never-truncate-a-file-you-still-need-to-read.md'
+
 emit() {
   jq -n --arg c "$RULE" \
     '{hookSpecificOutput: {hookEventName: "PreToolUse", additionalContext: $c}}'
 }
 
+emit_prepend() {
+  jq -n --arg c "$PREPEND_RULE" \
+    '{hookSpecificOutput: {hookEventName: "PreToolUse", additionalContext: $c}}'
+}
+
 case "$tool" in
   Grep)
     emit
     ;;
   Bash)
     cmd="$(printf '%s' "$input" | jq -r '.tool_input.command // ""')"
+    # Destructive-prepend shape: an open-for-write and a .read() of a file in
+    # the same command (Python one-liner or heredoc). Heuristic, non-blocking
+    # — false positives only cost an injected reminder.
+    if printf '%s' "$cmd" | grep -Eq 'open\([^)]*,[[:space:]]*\\*['"'"'"]w' \
+       && printf '%s' "$cmd" | grep -q '\.read()'; then
+      emit_prepend
     # Match grep/rg/sed/tail/head as a command word (start, or after a
     # pipe/semicolon/&&/whitespace), not as a substring of another word.
-    if printf '%s' "$cmd" | grep -Eq '(^|[|&;]|[[:space:]])(grep|rg|sed|tail|head)([[:space:]]|$)'; then
+    elif printf '%s' "$cmd" | grep -Eq '(^|[|&;]|[[:space:]])(grep|rg|sed|tail|head)([[:space:]]|$)'; then
       emit
     fi
     ;;

.claude/knowledge/never-truncate-a-file-you-still-need-to-read.md

@@ -0,0 +1,65 @@
+# Never open a file for writing in the same expression that still reads it
+
+> READ BY: every session and worker that writes any board, ledger, or
+> append-only file (`.claude/board/*`, `EPIPHANIES.md`, `PR_ARC_INVENTORY.md`,
+> plans, census docs) — and any executor running a scripted prepend.
+
+## Status: CONTRACT (locked by operator directive, 2026-08-30)
+
+Operator, verbatim: **"how about making that faulty one liner prohibited"** —
+after the pattern destroyed 5876 lines of `PR_ARC_INVENTORY.md`.
+
+## The One-Line Rule
+
+A file opened for writing/truncation may not be READ anywhere in the same
+expression, statement, or shell pipeline — prepend is read-into-variable →
+compose-in-memory → write, or the `Edit` tool (read-anchored by construction).
+
+## The incident (evidence class: observed)
+
+The #1081 board-hygiene commit ran:
+
+```python
+open(p, "w").write(entry + "\n" + open(p).read())   # PROHIBITED
+```
+
+Python evaluates `open(p, "w")` — truncating the file to zero bytes — before
+the argument's `open(p).read()` runs. The read-back returned `""`; the
+append-only ledger collapsed **5876 → 32 lines** on main, leaving a dangling
+#1079 self-reference as the visible wound. Restored same day in #1082
+(merge `82679c3a`), byte-identical from the parent blob `cdf8c15a^1`.
+
+## Consequences (all load-bearing)
+
+1. Prohibited in every language and shape: `sort f > f` (shell truncates `f`
+   before `sort` reads it), any Python expression combining `open(p, "w")`
+   with a read of `p`, any equivalent. Do not rely on remembering which
+   language evaluates arguments first — the rule is shape-based, not
+   language-based.
+2. Safe prepend is three steps: `body = read(p)` → compose → `write(p)`.
+   For board files the default is the `Edit` tool anyway.
+3. This is the sharper edge of the existing "Read before Write, always" P0:
+   read-before-write applies WITHIN a single expression's evaluation order,
+   not just across tool calls.
+
+## Falsifier (machine-runnable, mandatory after every ledger write)
+
+```bash
+wc -l <file>   # compare against the pre-write count
+```
+
+**An append-only file that got SHORTER is always a defect** — no exceptions.
+Supports: catching any truncation immediately. Does **not** prove: content
+correctness or ordering — a same-length corruption passes this check.
+
+A non-blocking PreToolUse guard (`.claude/hooks/anti-pattern-matching.sh`)
+injects this rule when a Bash command matches the write-while-reading shape.
+
+## Cross-reference / retrieval footer
+
+- Restore PR: lance-graph **#1082** (merge `82679c3a`); prohibition PR **#1083**
+  (merge `352005d3`); this file's Goldstandard-format landing: its own PR.
+- Board entry: `EPIPHANIES.md` `E-DESTRUCTIVE-PREPEND-TRUNCATES-BEFORE-READ-1`
+  (2026-08-30).
+- Census trap 10: `docs/architecture/COGNITIVE-FABRIC-CENSUS-2026-08-30.md` §8.3.
+- CLAUDE.md § In-Session Orchestration Discipline carries the short pointer.

CLAUDE.md

@@ -1395,24 +1395,15 @@ instead of *built from state*. If you see this on your own commit, you just
 overwrote committed work. Revert with `git restore <path>` and use `Edit`
 for any genuine refinement.
 
-**P0 Rule: the destructive-prepend one-liner is PROHIBITED**
-(added 2026-08-30 after it destroyed 5876 lines of `PR_ARC_INVENTORY.md`
-in #1081; restored in #1082; full entry
-`E-DESTRUCTIVE-PREPEND-TRUNCATES-BEFORE-READ-1`, census trap 10):
-
-```python
-open(p, "w").write(entry + open(p).read())   # NEVER — truncates before it reads
-```
-
-`open(p, "w")` truncates the file BEFORE the argument's `open(p).read()`
-runs; the read-back is empty and the file's history is gone. Prohibited in
-every form: any expression, statement, or shell pipeline that opens a file
-for writing/truncation while it still needs to READ that same file
-(`sort f > f` is the same defect). Prepend in three steps — read into a
-variable, compose in memory, write — or use the `Edit` tool, which is
-read-anchored by construction. **Mandatory post-check after every board /
-ledger write: `wc -l` the file. An append-only file that got SHORTER is
-always a defect.**
+**P0 Rule: the destructive-prepend one-liner is PROHIBITED** — never open a
+file for writing in the same expression/pipeline that still reads it
+(`open(p, "w").write(x + open(p).read())`, `sort f > f`). Mandatory
+post-check after every ledger write: `wc -l` — an append-only file that got
+SHORTER is always a defect. Full law, incident receipts (#1081/#1082),
+falsifier and consequences:
+`.claude/knowledge/never-truncate-a-file-you-still-need-to-read.md`
+(locked 2026-08-30; board entry
+`E-DESTRUCTIVE-PREPEND-TRUNCATES-BEFORE-READ-1`, census trap 10).
 
 **Tool-reach reminder for deferred tools.** `AskUserQuestion`, `TodoWrite`,
 `WebSearch`, `WebFetch` are namechecked in the Claude Code system prompt but