diff --git a/src/resources/extensions/sf/commands-debug.js b/src/resources/extensions/sf/commands-debug.js
index d2eb77502..737e5f57c 100644
--- a/src/resources/extensions/sf/commands-debug.js
+++ b/src/resources/extensions/sf/commands-debug.js
@@ -136,7 +136,7 @@ export async function handleDebug(args, ctx, pi) {
 				}
 			}
 		} catch (error) {
-			const message = error instanceof Error ? error.message : String(error);
+			const message = getErrorMessage(error);
 			ctx.ui.notify(
 				`Unable to create debug session: ${message}\nTry /debug --diagnose for artifact health details.`,
 				"error",
@@ -174,7 +174,7 @@ export async function handleDebug(args, ctx, pi) {
 			}
 			ctx.ui.notify(lines.join("\n"), "info");
 		} catch (error) {
-			const message = error instanceof Error ? error.message : String(error);
+			const message = getErrorMessage(error);
 			ctx.ui.notify(
 				`Unable to list debug sessions: ${message}\nRun /debug --diagnose for details.`,
 				"warning",
@@ -208,7 +208,7 @@ export async function handleDebug(args, ctx, pi) {
 				"info",
 			);
 		} catch (error) {
-			const message = error instanceof Error ? error.message : String(error);
+			const message = getErrorMessage(error);
 			ctx.ui.notify(
 				`Unable to load debug session '${parsed.slug}': ${message}\nTry /debug --diagnose ${parsed.slug}`,
 				"warning",
@@ -373,7 +373,7 @@ export async function handleDebug(args, ctx, pi) {
 				}
 			}
 		} catch (error) {
-			const message = error instanceof Error ? error.message : String(error);
+			const message = getErrorMessage(error);
 			ctx.ui.notify(
 				`Unable to continue debug session '${parsed.slug}': ${message}\nTry /debug --diagnose ${parsed.slug}`,
 				"warning",
@@ -427,7 +427,7 @@ export async function handleDebug(args, ctx, pi) {
 				}
 			}
 		} catch (error) {
-			const message = error instanceof Error ? error.message : String(error);
+			const message = getErrorMessage(error);
 			ctx.ui.notify(
 				`Unable to create diagnose session: ${message}\nTry /debug --diagnose for artifact health details.`,
 				"error",
@@ -484,7 +484,7 @@ export async function handleDebug(args, ctx, pi) {
 				listed.malformed.length > 0 ? "warning" : "info",
 			);
 		} catch (error) {
-			const message = error instanceof Error ? error.message : String(error);
+			const message = getErrorMessage(error);
 			ctx.ui.notify(`Diagnose failed: ${message}`, "error");
 		}
 	}
diff --git a/src/resources/extensions/sf/debug-session-store.js b/src/resources/extensions/sf/debug-session-store.js
index c95a99061..0916cabf9 100644
--- a/src/resources/extensions/sf/debug-session-store.js
+++ b/src/resources/extensions/sf/debug-session-store.js
@@ -2,6 +2,7 @@ import { existsSync, mkdirSync, readdirSync, readFileSync } from "node:fs";
 import { join } from "node:path";
 import { atomicWriteSync } from "./atomic-write.js";
 import { sfRoot } from "./paths.js";
+import { getErrorMessage } from "./error-utils.js";
 
 const DEFAULT_PHASE = "queued";
 const DEFAULT_STATUS = "active";
@@ -126,7 +127,7 @@ function parseDebugSessionArtifact(filePath, raw) {
 	try {
 		parsed = JSON.parse(raw);
 	} catch (error) {
-		const message = error instanceof Error ? error.message : String(error);
+		const message = getErrorMessage(error);
 		throw new Error(
 			`Failed to parse debug session artifact ${filePath}: ${message}`,
 		);
@@ -218,7 +219,7 @@ export function listDebugSessions(basePath, deps = {}) {
 		} catch (error) {
 			malformed.push({
 				artifactPath,
-				message: error instanceof Error ? error.message : String(error),
+				message: getErrorMessage(error),
 			});
 		}
 	}
diff --git a/src/resources/extensions/sf/doctor.js b/src/resources/extensions/sf/doctor.js
index 6f74b321e..41654b899 100644
--- a/src/resources/extensions/sf/doctor.js
+++ b/src/resources/extensions/sf/doctor.js
@@ -187,7 +187,7 @@ function parseJsonl(content) {
 		try {
 			JSON.parse(line);
 		} catch (error) {
-			const msg = error instanceof Error ? error.message : String(error);
+			const msg = getErrorMessage(error);
 			return `line ${i + 1}: ${msg}`;
 		}
 	}
@@ -206,7 +206,7 @@ function parseMarkdownFrontmatter(content) {
 		parseYaml(frontmatter);
 		return null;
 	} catch (error) {
-		return error instanceof Error ? error.message : String(error);
+		return getErrorMessage(error);
 	}
 }
 
@@ -295,7 +295,7 @@ function checkSfFormSyntax(basePath, issues, fixesApplied, shouldFix) {
 				parseError = parseMarkdownFrontmatter(content);
 			}
 		} catch (error) {
-			parseError = error instanceof Error ? error.message : String(error);
+			parseError = getErrorMessage(error);
 		}
 		if (parseError) {
 			const repaired = repairSfFormContent(ext, content);
diff --git a/src/resources/extensions/sf/production-mutation-approval.js b/src/resources/extensions/sf/production-mutation-approval.js
index 640fdd9e6..620db1f46 100644
--- a/src/resources/extensions/sf/production-mutation-approval.js
+++ b/src/resources/extensions/sf/production-mutation-approval.js
@@ -2,6 +2,7 @@ import { existsSync, readFileSync } from "node:fs";
 import { join } from "node:path";
 import { atomicWriteSync } from "./atomic-write.js";
 import { sfRoot } from "./paths.js";
+import { getErrorMessage } from "./error-utils.js";
 /** Schema version for production mutation approval JSON artifacts. */
 export const PRODUCTION_MUTATION_APPROVAL_SCHEMA_VERSION = 1;
 function unitId(unit) {
@@ -264,7 +265,7 @@ export function readProductionMutationApprovalStatus(basePath, unit) {
 		const result = validateProductionMutationApproval(data, unit);
 		return { path, approved: result.approved, reasons: result.reasons };
 	} catch (error) {
-		const message = error instanceof Error ? error.message : String(error);
+		const message = getErrorMessage(error);
 		return {
 			path,
 			approved: false,
diff --git a/src/resources/extensions/sf/worktree-command.js b/src/resources/extensions/sf/worktree-command.js
index 679329b49..730e05267 100644
--- a/src/resources/extensions/sf/worktree-command.js
+++ b/src/resources/extensions/sf/worktree-command.js
@@ -55,7 +55,7 @@ import {
 	getWorktreeOriginalCwd,
 	setWorktreeOriginalCwd,
 } from "./worktree-session-state.js";
-// ─── Shared completions and handler (used by both /worktree and /wt) ────────
+import { getErrorMessage } from "./error-utils.js";
 function worktreeCompletions(prefix) {
 	const parts = prefix.trim().split(/\s+/);
 	const subcommands = ["list", "merge", "remove", "switch", "create", "return"];
@@ -377,7 +377,7 @@ async function handleCreate(basePath, name, ctx) {
 			"info",
 		);
 	} catch (error) {
-		const msg = error instanceof Error ? error.message : String(error);
+		const msg = getErrorMessage(error);
 		ctx.ui.notify(`Failed to create worktree: ${msg}`, "error");
 	}
 }
@@ -421,7 +421,7 @@ async function handleSwitch(basePath, name, ctx) {
 			"info",
 		);
 	} catch (error) {
-		const msg = error instanceof Error ? error.message : String(error);
+		const msg = getErrorMessage(error);
 		ctx.ui.notify(`Failed to switch to worktree: ${msg}`, "error");
 	}
 }
@@ -549,7 +549,7 @@ async function handleList(basePath, ctx) {
 		}
 		ctx.ui.notify(lines.join("\n"), "info");
 	} catch (error) {
-		const msg = error instanceof Error ? error.message : String(error);
+		const msg = getErrorMessage(error);
 		ctx.ui.notify(`Failed to list worktrees: ${msg}`, "error");
 	}
 }
@@ -735,7 +735,7 @@ async function handleMerge(basePath, name, ctx, pi, targetBranch) {
 			"info",
 		);
 	} catch (error) {
-		const msg = error instanceof Error ? error.message : String(error);
+		const msg = getErrorMessage(error);
 		ctx.ui.notify(`Failed to start merge: ${msg}`, "error");
 	}
 }
@@ -774,7 +774,7 @@ async function handleRemove(basePath, name, ctx) {
 			"info",
 		);
 	} catch (error) {
-		const msg = error instanceof Error ? error.message : String(error);
+		const msg = getErrorMessage(error);
 		ctx.ui.notify(`Failed to remove worktree: ${msg}`, "error");
 	}
 }
@@ -824,7 +824,7 @@ async function handleRemoveAll(basePath, ctx) {
 			);
 		ctx.ui.notify(lines.join("\n"), failed.length > 0 ? "warning" : "info");
 	} catch (error) {
-		const msg = error instanceof Error ? error.message : String(error);
+		const msg = getErrorMessage(error);
 		ctx.ui.notify(`Failed to remove worktrees: ${msg}`, "error");
 	}
 }