fix(hooks): escape all JSON control characters in ai_memory_json_string (#732)

JSON forbids a raw control character (U+0000..U+001F) inside a string, but the
escaper covered only backslash, quote, tab and CR. A replayed tool result
carrying an ANSI colour escape (0x1b) reached stdout unescaped, so Claude Code
rejected the whole managed-workstream SessionStart packet as invalid JSON and
the session started with no context; any handoff summary with a control byte
failed the same way. Escape every other control byte as \u00XX with a linear
per-byte gsub pass, reusing #737's BusyBox replacement-doubling probe.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MDbhmszrjG9s5MrPrTuNtm

CHANGELOG.md

@@ -74,6 +74,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   reported `Updated` and failed to dedup its own prior Antigravity/Cursor/Kimi
   Code entries. It now matches both forms while still requiring the full
   `hook --event … --agent … --server-url …` argv signature (#740).
+- The POSIX shell hook bundle's `ai_memory_json_string` now escapes every JSON
+  control character (U+0000–U+001F) as `\u00XX`, not just backslash, quote, tab
+  and CR. A replayed tool result carrying an ANSI colour escape (0x1b) reached
+  stdout bare, so the managed-workstream SessionStart packet — and any handoff
+  whose summary held a control byte — was rejected as invalid JSON and the
+  resuming session started with no context. The escaping is linear and reuses
+  the same BusyBox replacement-doubling probe as the four existing escapes
+  (#732).
 
 ## [2.2.1] - 2026-09-12
 

hooks/_lib.sh

@@ -548,9 +548,26 @@ ai_memory_json_string() {
         BEGIN {
             probe = "X"; gsub(/X/, "\\\\", probe)
             if (length(probe) == 1) {
+                busybox = 1
                 BS = "\\\\\\\\"; QT = "\\\\\""; TB = "\\\\t"; CR = "\\\\r"
+                UP = "\\\\u"
             } else {
+                busybox = 0
                 BS = "\\\\"; QT = "\\\""; TB = "\\t"; CR = "\\r"
+                UP = "\\u"
+            }
+            # JSON forbids a raw control character (U+0000..U+001F) inside a
+            # string, but the four gsubs above only cover backslash, quote, tab
+            # and CR — so a replayed tool result carrying e.g. an ANSI colour
+            # escape (0x1b) reached stdout unescaped and Claude Code rejected
+            # the whole SessionStart packet as invalid JSON (#732). Build a
+            # \u00XX escape for every other control byte once; newline (0x0a) is
+            # never inside a record, it is the record separator handled below.
+            nc = 0
+            for (c = 1; c < 32; c++) {
+                if (c == 9 || c == 10 || c == 13) continue
+                cc[++nc] = sprintf("%c", c)
+                cr[nc] = sprintf("%s%04x", UP, c)
             }
             printf "\""
         }
@@ -559,6 +576,11 @@ ai_memory_json_string() {
             gsub(/"/, QT)
             gsub(/\t/, TB)
             gsub(/\r/, CR)
+            # After the backslash gsub, so the backslashes these introduce are
+            # not doubled. Each control byte is a literal (none is a regex
+            # metacharacter), and the pass is linear, not the per-char loop #727
+            # replaced.
+            for (k = 1; k <= nc; k++) gsub(cc[k], cr[k])
             printf "%s%s", sep, $0
             sep = "\\n"
         }

tests/hooks/test_lib.sh

@@ -169,6 +169,16 @@ next line'
 assert_eq "json_string escapes text" '"quoted \"thing\" \\ path\nnext line"' \
     "$(printf '%s' "$JSON_INPUT" | ai_memory_json_string)"
 
+# A raw control byte (JSON forbids U+0000..U+001F inside a string) must become
+# a \u00XX escape, not reach stdout bare -- a replayed ANSI-coloured tool
+# result otherwise made the whole SessionStart packet invalid JSON (#732).
+CTRL_OUT="$(printf 'a\033[0mb' | ai_memory_json_string)"
+case "$CTRL_OUT" in
+    *'\u001b'*) CTRL_ESCAPED=yes ;;
+    *) CTRL_ESCAPED=no ;;
+esac
+assert_eq "json_string escapes a control byte as a \u escape" "yes" "$CTRL_ESCAPED"
+
 # --- marker_qs --------------------------------------------------------
 QS=$(ai_memory_marker_qs "$TMP/a/b/c")
 assert_eq "marker_qs single key" "&cwd=$(ai_memory_url_encode "$TMP/a/b/c")&workspace=deep" "$QS"