diff --git a/hooks/session-start-seen-skills.mjs b/hooks/session-start-seen-skills.mjs
index 07736591..0aabc23e 100644
--- a/hooks/session-start-seen-skills.mjs
+++ b/hooks/session-start-seen-skills.mjs
@@ -11,7 +11,7 @@ import {
   removeAllSessionDedupArtifacts
 } from "./hook-env.mjs";
 import { createLogger } from "./logger.mjs";
-var CONTEXT_CLEARING_EVENTS = /* @__PURE__ */ new Set(["clear", "compact"]);
+var CONTEXT_CLEARING_SOURCES = /* @__PURE__ */ new Set(["clear", "compact"]);
 function parseSessionStartSeenSkillsInput(raw) {
   try {
     if (!raw.trim()) return null;
@@ -44,9 +44,9 @@ function main() {
     process.stdout.write(formatSessionStartSeenSkillsCursorOutput());
     return;
   }
-  const hookEvent = input?.hook_event_name ?? "";
+  const source = input?.source ?? "";
   const sessionId = input?.session_id ?? "";
-  const resetTriggered = CONTEXT_CLEARING_EVENTS.has(hookEvent) && !!sessionId;
+  const resetTriggered = CONTEXT_CLEARING_SOURCES.has(source) && !!sessionId;
   let removedFiles = 0;
   let removedDirs = 0;
   if (resetTriggered) {
@@ -55,7 +55,7 @@ function main() {
     removedDirs = result.removedDirs;
   }
   log.debug("session-start-seen-skills:decision", {
-    event: hookEvent || "unknown",
+    source: source || "unknown",
     sessionId: sessionId || "none",
     resetTriggered,
     removedFiles,
diff --git a/hooks/src/session-start-seen-skills.mts b/hooks/src/session-start-seen-skills.mts
index 3e7f4c46..25b7823f 100644
--- a/hooks/src/session-start-seen-skills.mts
+++ b/hooks/src/session-start-seen-skills.mts
@@ -29,11 +29,12 @@ interface SessionStartSeenSkillsInput {
   conversation_id?: string;
   cursor_version?: string;
   hook_event_name?: string;
+  source?: string;
   [key: string]: unknown;
 }
 
-/** Events where previously-injected skills are no longer in the context window. */
-const CONTEXT_CLEARING_EVENTS = new Set(["clear", "compact"]);
+/** Sources where previously-injected skills are no longer in the context window. */
+const CONTEXT_CLEARING_SOURCES = new Set(["clear", "compact"]);
 
 export function parseSessionStartSeenSkillsInput(raw: string): SessionStartSeenSkillsInput | null {
   try {
@@ -84,9 +85,9 @@ function main(): void {
   }
 
   // Claude Code: reset dedup state on clear/compact so skills get re-injected.
-  const hookEvent = input?.hook_event_name ?? "";
+  const source = input?.source ?? "";
   const sessionId = input?.session_id ?? "";
-  const resetTriggered = CONTEXT_CLEARING_EVENTS.has(hookEvent) && !!sessionId;
+  const resetTriggered = CONTEXT_CLEARING_SOURCES.has(source) && !!sessionId;
 
   let removedFiles = 0;
   let removedDirs = 0;
@@ -98,7 +99,7 @@ function main(): void {
   }
 
   log.debug("session-start-seen-skills:decision", {
-    event: hookEvent || "unknown",
+    source: source || "unknown",
     sessionId: sessionId || "none",
     resetTriggered,
     removedFiles,
diff --git a/tests/session-start-seen-skills.test.ts b/tests/session-start-seen-skills.test.ts
index dbbd2078..88d77da4 100644
--- a/tests/session-start-seen-skills.test.ts
+++ b/tests/session-start-seen-skills.test.ts
@@ -133,7 +133,7 @@ describe("session-start-seen-skills hook", () => {
       // Fire the hook with a "clear" event
       const result = await runSessionStart(
         { CLAUDE_ENV_FILE: undefined },
-        JSON.stringify({ session_id: sessionId, hook_event_name: "clear" }),
+        JSON.stringify({ session_id: sessionId, hook_event_name: "SessionStart", source: "clear" }),
       );
 
       expect(result.code).toBe(0);
@@ -161,7 +161,7 @@ describe("session-start-seen-skills hook", () => {
 
       const result = await runSessionStart(
         { CLAUDE_ENV_FILE: undefined },
-        JSON.stringify({ session_id: sessionId, hook_event_name: "compact" }),
+        JSON.stringify({ session_id: sessionId, hook_event_name: "SessionStart", source: "compact" }),
       );
 
       expect(result.code).toBe(0);
@@ -187,7 +187,7 @@ describe("session-start-seen-skills hook", () => {
       // 3. Fire "clear" event via session-start hook
       const result = await runSessionStart(
         { CLAUDE_ENV_FILE: undefined },
-        JSON.stringify({ session_id: sessionId, hook_event_name: "clear" }),
+        JSON.stringify({ session_id: sessionId, hook_event_name: "SessionStart", source: "clear" }),
       );
       expect(result.code).toBe(0);
 
@@ -213,7 +213,7 @@ describe("session-start-seen-skills hook", () => {
       // 3. Fire "compact" event via session-start hook
       const result = await runSessionStart(
         { CLAUDE_ENV_FILE: undefined },
-        JSON.stringify({ session_id: sessionId, hook_event_name: "compact" }),
+        JSON.stringify({ session_id: sessionId, hook_event_name: "SessionStart", source: "compact" }),
       );
       expect(result.code).toBe(0);
 
@@ -253,7 +253,7 @@ describe("session-start-seen-skills hook", () => {
       // Fire "clear" event
       const result = await runSessionStart(
         { CLAUDE_ENV_FILE: undefined },
-        JSON.stringify({ session_id: sessionId, hook_event_name: "clear" }),
+        JSON.stringify({ session_id: sessionId, hook_event_name: "SessionStart", source: "clear" }),
       );
       expect(result.code).toBe(0);
 
@@ -291,7 +291,7 @@ describe("session-start-seen-skills hook", () => {
 
       const result = await runSessionStart(
         { CLAUDE_ENV_FILE: undefined },
-        JSON.stringify({ session_id: sessionId, hook_event_name: "startup" }),
+        JSON.stringify({ session_id: sessionId, hook_event_name: "SessionStart", source: "startup" }),
       );
 
       expect(result.code).toBe(0);
@@ -304,6 +304,62 @@ describe("session-start-seen-skills hook", () => {
       try { rmSync(dedupFilePath(sessionId, "seen-skills")); } catch {}
     }
   });
+
+  test("test_clear_event_preserves_other_session_artifacts", async () => {
+    const sessionId = crypto.randomUUID();
+    const otherSessionId = crypto.randomUUID();
+
+    try {
+      expect(tryClaimSessionKey(sessionId, "seen-skills", "nextjs")).toBe(true);
+      expect(tryClaimSessionKey(otherSessionId, "seen-skills", "nextjs")).toBe(true);
+      expect(tryClaimSessionKey(otherSessionId, "seen-skills", "ai-sdk", "subagent-abc")).toBe(true);
+      writeFileSync(dedupFilePath(otherSessionId, "seen-skills"), "nextjs", "utf-8");
+
+      const result = await runSessionStart(
+        { CLAUDE_ENV_FILE: undefined },
+        JSON.stringify({ session_id: sessionId, hook_event_name: "SessionStart", source: "clear" }),
+      );
+
+      expect(result.code).toBe(0);
+      expect(existsSync(dedupClaimDirPath(sessionId, "seen-skills"))).toBe(false);
+      expect(existsSync(dedupClaimDirPath(otherSessionId, "seen-skills"))).toBe(true);
+      expect(existsSync(dedupClaimDirPath(otherSessionId, "seen-skills", "subagent-abc"))).toBe(true);
+      expect(readFileSync(dedupFilePath(otherSessionId, "seen-skills"), "utf-8")).toBe("nextjs");
+    } finally {
+      removeAllSessionDedupArtifacts(sessionId);
+      removeAllSessionDedupArtifacts(otherSessionId);
+    }
+  });
+
+  const preservingPayloads: Array<[string, (sessionId: string) => Record<string, unknown>]> = [
+    ["resume", (sessionId) => ({ session_id: sessionId, hook_event_name: "SessionStart", source: "resume" })],
+    ["unknown source", (sessionId) => ({ session_id: sessionId, hook_event_name: "SessionStart", source: "fork" })],
+    ["missing source", (sessionId) => ({ session_id: sessionId, hook_event_name: "SessionStart" })],
+    ["legacy hook_event_name clear", (sessionId) => ({ session_id: sessionId, hook_event_name: "clear" })],
+    ["legacy hook_event_name compact", (sessionId) => ({ session_id: sessionId, hook_event_name: "compact" })],
+    ["missing session_id", () => ({ hook_event_name: "SessionStart", source: "clear" })],
+    ["empty session_id", () => ({ session_id: "", hook_event_name: "SessionStart", source: "compact" })],
+    ["cursor payload", (sessionId) => ({ session_id: sessionId, conversation_id: "cursor-conversation", source: "clear" })],
+  ];
+
+  for (const [name, payload] of preservingPayloads) {
+    test(`test_${name.replaceAll(" ", "_")}_preserves_claim_dir`, async () => {
+      const sessionId = crypto.randomUUID();
+
+      try {
+        expect(tryClaimSessionKey(sessionId, "seen-skills", "nextjs")).toBe(true);
+        writeFileSync(dedupFilePath(sessionId, "seen-skills"), "nextjs", "utf-8");
+
+        const result = await runSessionStart({ CLAUDE_ENV_FILE: undefined }, JSON.stringify(payload(sessionId)));
+
+        expect(result.code).toBe(0);
+        expect(existsSync(dedupClaimDirPath(sessionId, "seen-skills"))).toBe(true);
+        expect(readFileSync(dedupFilePath(sessionId, "seen-skills"), "utf-8")).toBe("nextjs");
+      } finally {
+        removeAllSessionDedupArtifacts(sessionId);
+      }
+    });
+  }
 });
 
 describe("hook-env session temp path guards", () => {