diff --git a/Sources/App/DeckardHooksInstaller.swift b/Sources/App/DeckardHooksInstaller.swift
index 110b5f8..6985210 100644
--- a/Sources/App/DeckardHooksInstaller.swift
+++ b/Sources/App/DeckardHooksInstaller.swift
@@ -14,25 +14,32 @@ enum DeckardHooksInstaller {
         [ -z "$DECKARD_SOCKET_PATH" ] && exit 0
 
         EVENT="$1"
-        cat > /dev/null  # drain stdin (hooks don't carry rate_limits)
+        INPUT=$(cat)
         EXTRA=""
 
-        # For session-start, walk parent PIDs to find the Claude session ID
+        # For session-start, extract the session ID so Deckard can find the JSONL transcript.
+        # Primary: read session_id from stdin JSON (works for both new and resumed sessions).
+        # Fallback: walk parent PIDs to find ~/.claude/sessions/<pid>.json (original method,
+        #           unreliable for resumed sessions but better than nothing if stdin is empty).
         if [ "$EVENT" = "session-start" ]; then
-            PID=$$
-            CWD="$(pwd)"
-            for _ in 1 2 3 4 5; do
-                PID=$(ps -o ppid= -p "$PID" 2>/dev/null | tr -d ' ')
-                [ -z "$PID" ] || [ "$PID" = "1" ] && break
-                SESSION_FILE="$HOME/.claude/sessions/${PID}.json"
-                if [ -f "$SESSION_FILE" ]; then
-                    FILE_CWD=$(python3 -c "import json,sys; print(json.load(open(sys.argv[1])).get('cwd',''))" "$SESSION_FILE" 2>/dev/null)
-                    if [ "$FILE_CWD" = "$CWD" ]; then
-                        SID=$(python3 -c "import json,sys; print(json.load(open(sys.argv[1]))['sessionId'])" "$SESSION_FILE" 2>/dev/null)
-                        [ -n "$SID" ] && EXTRA=",\\"sessionId\\":\\"$SID\\"" && break
+            SID=$(printf '%s' "$INPUT" | python3 -c "import json,sys; print(json.load(sys.stdin).get('session_id',''))" 2>/dev/null)
+            if [ -z "$SID" ]; then
+                PID=$$
+                CWD="$(pwd)"
+                for _ in 1 2 3 4 5; do
+                    PID=$(ps -o ppid= -p "$PID" 2>/dev/null | tr -d ' ')
+                    [ -z "$PID" ] || [ "$PID" = "1" ] && break
+                    SESSION_FILE="$HOME/.claude/sessions/${PID}.json"
+                    if [ -f "$SESSION_FILE" ]; then
+                        FILE_CWD=$(python3 -c "import json,sys; print(json.load(open(sys.argv[1])).get('cwd',''))" "$SESSION_FILE" 2>/dev/null)
+                        if [ "$FILE_CWD" = "$CWD" ]; then
+                            SID=$(python3 -c "import json,sys; print(json.load(open(sys.argv[1]))['sessionId'])" "$SESSION_FILE" 2>/dev/null)
+                            break
+                        fi
                     fi
-                fi
-            done
+                done
+            fi
+            [ -n "$SID" ] && EXTRA=",\\"sessionId\\":\\"$SID\\""
         fi
 
         printf '{"command":"hook.%s","surfaceId":"%s"%s}\\n' "$EVENT" "$DECKARD_SURFACE_ID" "$EXTRA" \\
diff --git a/Sources/Window/DeckardWindowController.swift b/Sources/Window/DeckardWindowController.swift
index dd6665a..6fca1ca 100644
--- a/Sources/Window/DeckardWindowController.swift
+++ b/Sources/Window/DeckardWindowController.swift
@@ -1122,19 +1122,15 @@ class DeckardWindowController: NSWindowController, NSSplitViewDelegate {
 
     func updateSessionId(forSurfaceId surfaceIdStr: String, sessionId: String) {
         guard let tab = tabForSurfaceId(surfaceIdStr) else { return }
-        // Only set the session ID if the tab doesn't already have one.
-        // Resumed sessions report a new ID in ~/.claude/sessions/<pid>.json
-        // that doesn't correspond to an actual JSONL session file.
-        if tab.sessionId == nil || tab.sessionId!.isEmpty {
-            tab.sessionId = sessionId
-            SessionManager.shared.saveSessionName(sessionId: sessionId, name: tab.name)
-            saveState()
-            // Start watching if this is the currently displayed tab
-            if let project = currentProject,
-               let idx = project.tabs.firstIndex(where: { $0.id == tab.id }),
-               idx == project.selectedTabIndex {
-                refreshContextBar(for: tab)
-            }
+        guard tab.sessionId != sessionId else { return }
+        tab.sessionId = sessionId
+        SessionManager.shared.saveSessionName(sessionId: sessionId, name: tab.name)
+        saveState()
+        // Start watching if this is the currently displayed tab
+        if let project = currentProject,
+           let idx = project.tabs.firstIndex(where: { $0.id == tab.id }),
+           idx == project.selectedTabIndex {
+            refreshContextBar(for: tab)
         }
     }
 
diff --git a/Tests/DeckardHooksInstallerTests.swift b/Tests/DeckardHooksInstallerTests.swift
index 9a7c64b..fd3bf8a 100644
--- a/Tests/DeckardHooksInstallerTests.swift
+++ b/Tests/DeckardHooksInstallerTests.swift
@@ -416,4 +416,79 @@ final class DeckardHooksInstallerTests: XCTestCase {
             XCTAssertFalse(marker.isEmpty, "Marker '\(marker)' should be non-empty")
         }
     }
+
+    // MARK: - Hook script reads session_id from stdin with PID walking fallback
+
+    func testHookScriptReadsSessionIdFromStdin() throws {
+        let tempDir = NSTemporaryDirectory() + "deckard-hooks-test-\(UUID().uuidString)/"
+        let hooksDir = tempDir + "hooks/"
+        try FileManager.default.createDirectory(atPath: hooksDir, withIntermediateDirectories: true)
+        addTeardownBlock { try? FileManager.default.removeItem(atPath: tempDir) }
+
+        let hookPath = hooksDir + "notify.sh"
+        let statusLinePath = hooksDir + "statusline.sh"
+        DeckardHooksInstaller.installHookScript(
+            hookScriptPath: hookPath,
+            statusLineScriptPath: statusLinePath
+        )
+
+        let content = try String(contentsOfFile: hookPath, encoding: .utf8)
+
+        // Must read stdin into a variable (not drain it)
+        XCTAssertTrue(content.contains("INPUT=$(cat)"),
+                       "Hook script should capture stdin into INPUT variable")
+        XCTAssertFalse(content.contains("cat > /dev/null"),
+                        "Hook script must not drain stdin — session_id comes from it")
+
+        // Must extract session_id from stdin JSON for session-start
+        XCTAssertTrue(content.contains("session_id"),
+                       "Hook script should extract session_id from stdin JSON")
+    }
+
+    func testHookScriptFallsBackToPidWalking() throws {
+        let tempDir = NSTemporaryDirectory() + "deckard-hooks-test-\(UUID().uuidString)/"
+        let hooksDir = tempDir + "hooks/"
+        try FileManager.default.createDirectory(atPath: hooksDir, withIntermediateDirectories: true)
+        addTeardownBlock { try? FileManager.default.removeItem(atPath: tempDir) }
+
+        let hookPath = hooksDir + "notify.sh"
+        let statusLinePath = hooksDir + "statusline.sh"
+        DeckardHooksInstaller.installHookScript(
+            hookScriptPath: hookPath,
+            statusLineScriptPath: statusLinePath
+        )
+
+        let content = try String(contentsOfFile: hookPath, encoding: .utf8)
+
+        // PID walking should still exist as fallback when stdin doesn't contain session_id
+        XCTAssertTrue(content.contains("ppid"),
+                       "Hook script should fall back to PID walking when stdin has no session_id")
+        XCTAssertTrue(content.contains(".claude/sessions/"),
+                       "Hook script should check session files as fallback")
+    }
+
+    func testHookScriptTriesStdinBeforePidWalking() throws {
+        let tempDir = NSTemporaryDirectory() + "deckard-hooks-test-\(UUID().uuidString)/"
+        let hooksDir = tempDir + "hooks/"
+        try FileManager.default.createDirectory(atPath: hooksDir, withIntermediateDirectories: true)
+        addTeardownBlock { try? FileManager.default.removeItem(atPath: tempDir) }
+
+        let hookPath = hooksDir + "notify.sh"
+        let statusLinePath = hooksDir + "statusline.sh"
+        DeckardHooksInstaller.installHookScript(
+            hookScriptPath: hookPath,
+            statusLineScriptPath: statusLinePath
+        )
+
+        let content = try String(contentsOfFile: hookPath, encoding: .utf8)
+
+        // stdin extraction must come BEFORE PID walking
+        guard let stdinPos = content.range(of: "session_id")?.lowerBound,
+              let pidPos = content.range(of: "ppid")?.lowerBound else {
+            XCTFail("Script must contain both session_id extraction and ppid fallback")
+            return
+        }
+        XCTAssertTrue(stdinPos < pidPos,
+                       "Hook script should try stdin session_id before falling back to PID walking")
+    }
 }