hooks/lib/subagent.ts: CLAUDE_CODE_FORK_SUBAGENT is set in main sessions on Claude Code 2.1.26x+, muting nine hooks (fix + tests attached)

diff --git i/LifeOS/install/hooks/lib/subagent.ts w/LifeOS/install/hooks/lib/subagent.ts
index b3a031e..6858b7a 100644
--- i/LifeOS/install/hooks/lib/subagent.ts
+++ w/LifeOS/install/hooks/lib/subagent.ts
@@ -1,4 +1,5 @@
 /**
+ * @version 2.0.0
  * subagent.ts — the single answer to "am I running inside a subagent?"
  *
  * Eight hooks each carried their own copy of this test, and the copies had
@@ -12,25 +13,47 @@
  * because nothing compares them; one function is the fix, not a rule telling
  * people to keep nine copies in step.
  *
- * The test is the UNION of every known marker. That is strictly safer than any
- * single family: a missed subagent leaks main-session context (and a duplicate
- * surface line) into a delegate, while a false positive would suppress context
- * in a main session. Verified 2026-07-28 in a main session — every marker below
- * is unset, so the union cannot false-positive there.
+ * v2.0.0 (2026-09-18, INC-20260918-hook-mute): the documented signal comes
+ * first. Claude Code puts `agent_id` (and `agent_type`) in the hook's stdin
+ * JSON when, and only when, the hook runs inside a subagent (hooks reference:
+ * "When running with --agent or inside a subagent, two additional fields are
+ * included"). Callers that have parsed their stdin pass it in; the env markers
+ * remain as the fallback for callers with no stdin.
+ *
+ * The one marker that is GONE is `CLAUDE_CODE_FORK_SUBAGENT`. It was added
+ * for public issue #1831 (forks set only that marker). From Claude Code
+ * 2.1.26x the harness exports it into EVERY child of the main interactive
+ * session — hooks included, verified on a live PostToolUse hook process on
+ * 2.1.274 — so keying on it muted nine hooks in every primary session for
+ * four days before anyone noticed. A false positive here suppresses the
+ * session-start context, the hot-layer memory, the //⚙️ lines, the ascent
+ * strip and the memory reviewer, silently. Never key on an undocumented
+ * env variable again; the stdin field is the contract.
  */
 
-/** True when this process is a subagent/delegate rather than the main session. */
-export function isSubagentContext(): boolean {
+/** The two fields Claude Code adds to hook stdin inside a subagent. */
+export interface SubagentIdentity {
+  agent_id?: unknown;
+  agent_type?: unknown;
+}
+
+/**
+ * True when this process is a subagent/delegate rather than the main session.
+ *
+ * @param input the hook's parsed stdin JSON, when the caller has it. A hook
+ *   that has not read stdin passes nothing and gets the env-only answer.
+ */
+export function isSubagentContext(input?: SubagentIdentity | null): boolean {
+  if (input && typeof input === 'object') {
+    if (typeof input.agent_id === 'string' && input.agent_id.length > 0) return true;
+    if (typeof input.agent_type === 'string' && input.agent_type.length > 0) return true;
+  }
   const projectDir = process.env.CLAUDE_PROJECT_DIR || '';
   return Boolean(
     projectDir.includes('/.claude/Agents/') ||
       process.env.CLAUDE_AGENT_TYPE ||
       process.env.CLAUDE_CODE_SUBAGENT_NAME ||
       process.env.CLAUDE_CODE_SUBAGENT_TYPE ||
-      // Forked subagents set ONLY the fork marker — none of the above.
-      // Without it, 8 hook consumers re-inject main-session context into
-      // forks that inherited it via cache. (public issue #1831, @DRAZY)
-      process.env.CLAUDE_CODE_FORK_SUBAGENT === '1' ||
       process.env.CLAUDE_AGENT_SDK === '1',
   );
 }