fix: nested template literals in step inputs, and unresolvable $args tags (#10856)

* fix(frontend): keep nested template literals intact in template inputs Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: fail a flow step with an unresolvable $args tag instead of hanging Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): surface input expression errors when running a step test Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): treat an escaped \${ as literal text when escaping backticks Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: accept the string "null" as a tag component, reject only JSON null Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: leave a same_worker step's inert tag alone, log an unresolved flow tag Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): escape every backtick when the template walk desynchronizes Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: leave a dedicated runnable's inert step tag alone Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: reroute a step only when its own tag is what failed to resolve Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * refactor: name the inert-tag guard step_is_pulled_by_tag Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: reject a tag only when it interpolates to nothing at all Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): validate the template walk instead of trusting a balanced stack Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * docs: describe what an unresolvable tag actually interpolates to Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * refactor(frontend): decide template escaping with a real parser, not a hand-rolled scan Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * refactor: name is_flow_step on push now that it is load-bearing Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): heal an expression escaped before nested templates were handled Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: reroute a step whose tag reads args that failed to evaluate Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: never hand a job that failed before running to a dedicated runner Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: reroute only a step whose args failed, leave other tags untouched Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix: drop the post-preprocessor tag fallback, leaving tag resolution untouched Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * refactor: leave interpolate_args exactly as it was Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * test: use a generic example in the template literal tests Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): show an expression escaped by the old rule as it was authored Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): surface input expression errors from every step-run entry point Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * docs: state what is_dedicated_worker actually reads Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): heal only text whose backticks were all escaped by the old rule Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): match the old rule textually so an authored backslash still heals Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> * fix(frontend): heal only expressions the old rule broke, never ones that parse Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
2026-09-05 08:02:18 +00:00 · 2026-08-28 16:27:54 +02:00
parent 9213319a74
commit 8f349c032a
14 changed files with 289 additions and 69 deletions
@@ -4671,6 +4671,12 @@ pub async fn check_debouncing_within_limits(
    }
 }

+/// Whether the tag's queue name is computed from the job's arguments, so that a caller holding
+/// arguments it could not build knows the tag cannot be built either.
+pub fn tag_reads_args(tag: &str) -> bool {
+    RE_ARG_TAG.is_match(tag)
+}
+
 pub fn interpolate_args(x: String, args: &PushArgs, workspace_id: &str) -> String {
    // Save this value to avoid parsing twice
    let workspaced = x.as_str().replace("$workspace", workspace_id).to_string();
@@ -632,6 +632,28 @@ pub enum JobPayload {
    },
 }

+impl JobPayload {
+    /// Whether the payload itself declares a dedicated worker, in which case `push` replaces
+    /// whatever tag it is handed and the caller's tag never reaches the queue.
+    ///
+    /// This reads what the payload carries, not what `push` will conclude: a `SingleStepFlow`
+    /// loads the flag from the script row at push time and reports `false` here. That only
+    /// matters to a caller reasoning about the tag, and for those the answer is the same either
+    /// way, since `push` replaces the tag in exactly the case this misses.
+    pub fn is_dedicated_worker(&self) -> bool {
+        let dedicated_worker = match self {
+            JobPayload::ScriptHash { dedicated_worker, .. }
+            | JobPayload::FlowScript { dedicated_worker, .. }
+            | JobPayload::Dependencies { dedicated_worker, .. }
+            | JobPayload::FlowDependencies { dedicated_worker, .. }
+            | JobPayload::Flow { dedicated_worker, .. } => dedicated_worker,
+            JobPayload::Code(raw) => &raw.dedicated_worker,
+            _ => &None,
+        };
+        dedicated_worker.is_some_and(|x| x)
+    }
+}
+
 #[derive(Clone, Serialize, Deserialize, Debug)]
 pub struct SkipHandler {
    pub path: String,
@@ -3532,7 +3532,13 @@ pub async fn run_worker(
                    job.kind,
                    JobKind::Script | JobKind::Preview | JobKind::FlowScript
                ) {
-                    if !dedicated_workers.is_empty() {
+                    // A job carrying a pre-run error never runs its code: it only has to be
+                    // pulled so `handle_queued_job` can fail it. Both hand-off paths below
+                    // dispatch by path and return before that check, so a job sent down them
+                    // would run with whatever arguments survived the failure.
+                    let fails_before_running = job.pre_run_error.is_some();
+
+                    if !dedicated_workers.is_empty() && !fails_before_running {
                        let dedicated_worker_tx = job.runnable_path.as_ref().and_then(|path| {
                            // For flow steps inside branches/loops, runnable_path includes
                            // nesting segments (e.g. f/flow/branchone-0/a) but the dedicated
@@ -3577,7 +3583,7 @@ pub async fn run_worker(
                        NextJob::Http(_) => None,
                    };

-                    if let Some(flow_runners) = flow_runners {
+                    if let Some(flow_runners) = flow_runners.filter(|_| !fails_before_running) {
                        let key_o = job.flow_step_id.as_ref().map(|x| x.to_string());
                        if let Some(key) = key_o {
                            if let Some(flow_runner_tx) = flow_runners.runners.get(&key) {
@@ -70,9 +70,9 @@ use windmill_queue::schedule::get_schedule_opt;
 use windmill_queue::{
    add_completed_job, add_completed_job_error, append_logs, get_mini_pulled_job,
    insert_concurrency_key_capped, interpolate_args,
-    report_error_to_workspace_handler_or_critical_side_channel, try_schedule_next_job, CanceledBy,
-    FlowRunners, MiniCompletedJob, MiniPulledJob, PushArgs, PushIsolationLevel, SameWorkerPayload,
-    WrappedError,
+    report_error_to_workspace_handler_or_critical_side_channel, tag_reads_args,
+    try_schedule_next_job, CanceledBy, FlowRunners, MiniCompletedJob, MiniPulledJob, PushArgs,
+    PushIsolationLevel, SameWorkerPayload, WrappedError,
 };

 use windmill_audit::audit_oss::audit_log;
@@ -4403,6 +4403,23 @@ async fn push_next_flow_job(
            payload_tag.tag.as_deref(),
        );

+        // `push_args` is empty once the input transforms failed, so a tag reading `$args[...]`
+        // interpolates to a queue nobody serves and the step sits there instead of reporting
+        // the error. Send it to the flow's tag, which a worker is provably serving right now.
+        //
+        // A step handed over by id, or one whose tag `push` replaces, never reaches a worker
+        // through its tag, so rewriting theirs would be noise.
+        let step_is_pulled_by_tag = !continue_on_same_worker
+            && !continue_with_runners
+            && !payload_tag.payload.is_dedicated_worker();
+        let reroute_to_flow_tag =
+            err.is_some() && step_is_pulled_by_tag && tag.as_deref().is_some_and(tag_reads_args);
+        let tag = if reroute_to_flow_tag {
+            Some(flow_job.tag.clone())
+        } else {
+            tag
+        };
+
        let (email, permissioned_as) = if let Some(on_behalf_of) = payload_tag.on_behalf_of.as_ref()
        {
            (&on_behalf_of.email, on_behalf_of.permissioned_as.clone())
@@ -4421,8 +4438,7 @@ async fn push_next_flow_job(
            .as_deref()
            .filter(|t| !t.is_empty() && *t != flow_job.tag.as_str())
        {
-            let is_super_admin =
-                windmill_common::auth::is_super_admin_email(db, email).await?;
+            let is_super_admin = windmill_common::auth::is_super_admin_email(db, email).await?;
            check_tag_available_for_workspace_internal(
                db,
                &flow_job.workspace_id,
@@ -6155,9 +6171,7 @@ pub async fn script_to_payload(
                .await?
                .prefetch_cached(&db)
                .await?;
-            let on_behalf_of = script_info
-                .on_behalf_of(&flow_job.workspace_id, db)
-                .await?;
+            let on_behalf_of = script_info.on_behalf_of(&flow_job.workspace_id, db).await?;
            let ScriptHashInfo {
                tag,
                cache_ttl,
@@ -29,6 +29,7 @@
 				"@windmill-labs/svelte-dnd-action": "^0.9.44",
 				"@xterm/addon-fit": "^0.10.0",
 				"@xyflow/svelte": "^1.0.0",
+				"acorn": "^8.15.0",
 				"ag-charts-community": "^9.0.1",
 				"ag-charts-enterprise": "^9.0.1",
 				"ag-grid-community": "^31.3.4",
@@ -1754,7 +1755,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1771,7 +1771,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1788,7 +1787,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1805,7 +1803,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1822,7 +1819,6 @@
 			"cpu": [
 				"arm"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1839,7 +1835,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1856,7 +1851,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1873,7 +1867,6 @@
 			"cpu": [
 				"ppc64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1890,7 +1883,6 @@
 			"cpu": [
 				"s390x"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1907,7 +1899,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1924,7 +1915,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1941,7 +1931,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1958,7 +1947,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -1975,7 +1963,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MIT",
 			"optional": true,
 			"os": [
@@ -7582,7 +7569,7 @@
 			"version": "1.21.7",
 			"resolved": "https://registry.npmjs.org/jiti/-/jiti-1.21.7.tgz",
 			"integrity": "sha512-/imKNG4EbWNrVjoNC/1H5/9GFy+tqjGBHCaSsN+P2RnPqjsLmv6UD3Ej+Kj8nBWaRAwyk7kK5ZUc+OEatnTR3A==",
-			"dev": true,
+			"devOptional": true,
 			"license": "MIT",
 			"bin": {
 				"jiti": "bin/jiti.js"
@@ -8278,7 +8265,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8299,7 +8285,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8320,7 +8305,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8341,7 +8325,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8362,7 +8345,6 @@
 			"cpu": [
 				"arm"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8383,7 +8365,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8404,7 +8385,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8425,7 +8405,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8446,7 +8425,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8467,7 +8445,6 @@
 			"cpu": [
 				"arm64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -8488,7 +8465,6 @@
 			"cpu": [
 				"x64"
 			],
-			"dev": true,
 			"license": "MPL-2.0",
 			"optional": true,
 			"os": [
@@ -13194,21 +13170,6 @@
 				}
 			}
 		},
-		"node_modules/svelte-check/node_modules/picomatch": {
-			"version": "4.0.5",
-			"resolved": "https://registry.npmjs.org/picomatch/-/picomatch-4.0.5.tgz",
-			"integrity": "sha512-RvwwcruNjI1ncT5xRakeyS9Lf8lcItv34KD+aif+VH9kduAyfYBipGh12274xtenIPZ119/R9BdTBa8gAwSh0A==",
-			"dev": true,
-			"license": "MIT",
-			"optional": true,
-			"peer": true,
-			"engines": {
-				"node": ">=12"
-			},
-			"funding": {
-				"url": "https://github.com/sponsors/jonschlinkert"
-			}
-		},
 		"node_modules/svelte-eslint-parser": {
 			"version": "0.43.0",
 			"resolved": "https://registry.npmjs.org/svelte-eslint-parser/-/svelte-eslint-parser-0.43.0.tgz",
@@ -13988,7 +13949,7 @@
 			"version": "5.9.3",
 			"resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",
 			"integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
-			"dev": true,
+			"devOptional": true,
 			"license": "Apache-2.0",
 			"bin": {
 				"tsc": "bin/tsc",
@@ -105,6 +105,7 @@
 		"@windmill-labs/svelte-dnd-action": "^0.9.44",
 		"@xterm/addon-fit": "^0.10.0",
 		"@xyflow/svelte": "^1.0.0",
+		"acorn": "^8.15.0",
 		"ag-charts-community": "^9.0.1",
 		"ag-charts-enterprise": "^9.0.1",
 		"ag-grid-community": "^31.3.4",
@@ -30,6 +30,7 @@
 	import type { InputTransform } from '$lib/gen'
 	import TemplateEditor from './TemplateEditor.svelte'
 	import { setInputCat as computeInputCat, isCodeInjection } from '$lib/utils'
+	import { escapeTemplateBackticks } from '$lib/utils/templateLiteral'
 	import { FunctionSquare, InfoIcon } from 'lucide-svelte'
 	import { getResourceTypes } from './resourceTypesStore'
 	import type { FlowCopilotContext } from './copilot/flow'
@@ -253,7 +254,7 @@
 			arg.expr = getDefaultExpr(
 				argName,
 				previousModuleId,
-				`\`${rawValue.toString().replaceAll('`', '\\`')}\``
+				`\`${escapeTemplateBackticks(rawValue.toString())}\``
 			)
 			arg.type = 'javascript'
 			propertyType = 'static'
@@ -687,7 +688,7 @@
 											argName,
 											previousModuleId,
 											staticTemplate
-												? `\`${arg?.value?.toString().replaceAll('`', '\\`') ?? ''}\``
+												? `\`${escapeTemplateBackticks(arg?.value?.toString() ?? '')}\``
 												: arg.value
 													? '(' + JSON.stringify(arg?.value, null, 4) + ')'
 													: ''
@@ -50,14 +50,19 @@
 	let jobProgressReset: () => void = () => {}
 	let stepHistoryLoader = getStepHistoryLoaderContext()

+	// Every explicit run re-evaluates the args with errors surfaced. The reactive evaluations
+	// that follow each flow edit stay quiet, so without this a failing expression is silently
+	// `undefined` in what the run is built from. Manually edited args are preserved across the
+	// refresh by `initializeFromSchema`.
 	export function runTestWithStepArgs() {
-		const args = stepsInputArgs.getStepArgs(mod.id)
-		runTest(args)
-	}
-
-	export function loadArgsAndRunTest() {
-		stepsInputArgs?.updateStepArgs(mod.id, flowStateStore.val, flowStore?.val, previewArgs?.val)
-		runTestWithStepArgs()
+		stepsInputArgs?.updateStepArgs(
+			mod.id,
+			flowStateStore.val,
+			flowStore?.val,
+			previewArgs?.val,
+			true
+		)
+		runTest(stepsInputArgs.getStepArgs(mod.id))
 	}

 	// A step's timeout is an InputTransform. Only a static numeric value can be applied
@@ -19,6 +19,7 @@
 	import { computeGlobalContext, eval_like } from './eval'
 	import { deepEqual } from 'fast-equals'
 	import { deepMergeWithPriority, isCodeInjection, readFieldsRecursively } from '$lib/utils'
+	import { escapeTemplateBackticks } from '$lib/utils/templateLiteral'
 	import sum from 'hash-sum'
 	import { createDispatcherIfMounted } from '$lib/createDispatcherIfMounted'

@@ -271,7 +272,7 @@
 		if ((input.type === 'template' || input.type == 'templatev2') && isCodeInjection(input.eval)) {
 			try {
 				const r = await eval_like(
-					'`' + input.eval.replaceAll('`', '\\`') + '`',
+					'`' + escapeTemplateBackticks(input.eval) + '`',
 					computeGlobalContext($worldStore, id, fullContext),
 					$stateStore,
 					$mode == 'dnd',
@@ -464,7 +464,7 @@
 							btnClasses="px-1 py-1.5 bg-surface"
 							on:click={() => {
 								outputPicker?.toggleOpen(true)
-								moduleTest?.loadArgsAndRunTest()
+								moduleTest?.runTestWithStepArgs()
 							}}
 							dropdownItems={[
 								{
@@ -125,12 +125,15 @@ export class StepsInputArgs {
 	initializeFromSchema(
 		mod: FlowModule,
 		schema: { properties?: Record<string, any> },
-		pickableProperties: PickableProperties | undefined
+		pickableProperties: PickableProperties | undefined,
+		// Off for the reactive re-evaluations that follow every flow edit; on for an explicit
+		// run, where a failing expression would otherwise become `undefined` unseen.
+		showError: boolean = false
 	) {
 		const args = Object.fromEntries(
 			Object.keys(schema.properties ?? {}).map((k) => [
 				k,
-				evalValue(k, mod, pickableProperties, false)
+				evalValue(k, mod, pickableProperties, showError)
 			])
 		)

@@ -158,14 +161,16 @@ export class StepsInputArgs {
 		id: string,
 		flowState: FlowState | undefined,
 		flow: OpenFlow | undefined,
-		previewArgs: Record<string, any> | undefined
+		previewArgs: Record<string, any> | undefined,
+		showError: boolean = false
 	) {
 		if (id === 'failure' && flow && flow.value.failure_module && flowState) {
 			const picker = getFailureStepPropPicker(flowState, flow, previewArgs)
 			this.initializeFromSchema(
 				flow.value.failure_module,
 				flowState['failure']?.schema ?? {},
-				picker.pickableProperties
+				picker.pickableProperties,
+				showError
 			)
 			return
 		}
@@ -193,7 +198,12 @@ export class StepsInputArgs {
 			false
 		)
 		const pickableProperties = stepPropPicker.pickableProperties
-		this.initializeFromSchema(modules[0], flowState[id]?.schema ?? {}, pickableProperties)
+		this.initializeFromSchema(
+			modules[0],
+			flowState[id]?.schema ?? {},
+			pickableProperties,
+			showError
+		)
 	}

 	removeExtraKey(moduleId: string, keys: string[]) {
@@ -12,6 +12,7 @@ import {
 } from '$lib/gen'
 import { workspaceStore } from '$lib/stores'
 import { cleanExpr, emptySchema } from '$lib/utils'
+import { unescapeTemplateBackticks } from '$lib/utils/templateLiteral'
 import { get } from 'svelte/store'
 import type { FlowModuleState } from './flowState'
 import { type PickableProperties, dfs } from './previousResults'
@@ -219,7 +220,7 @@ export function codeToStaticTemplate(code?: string): string | undefined {
 	if (lines.length == 1) {
 		const line = lines[0].trim()
 		if (line[0] == '`' && line.charAt(line.length - 1) == '`') {
-			return line.slice(1, line.length - 1).replaceAll('\\`', '`')
+			return unescapeTemplateBackticks(line.slice(1, line.length - 1))
 		} else {
 			return `\$\{${line}\}`
 		}
@@ -0,0 +1,133 @@
+import { describe, it, expect } from 'vitest'
+import { escapeTemplateBackticks, unescapeTemplateBackticks } from './templateLiteral'
+
+// Template mode stores its value as a JS template literal, so backticks in the text have to be
+// escaped. Escaping them inside `${...}` too is what broke nested template literals: a backslash
+// is a syntax error in expression position.
+describe('escapeTemplateBackticks', () => {
+	const nested =
+		'--input ${flow_input.iter.value}${results.config ? ` --config ${results.config}` : ""} --host ${flow_input.hostname}'
+
+	it('leaves a nested template literal inside an interpolation intact', () => {
+		const expr = '`' + escapeTemplateBackticks(nested) + '`'
+		expect(expr).not.toContain('\\`')
+		expect(
+			new Function('flow_input', 'results', 'return ' + expr)(
+				{ iter: { value: 'data.csv' }, hostname: 'host1' },
+				{ config: '/tmp/cfg.json' }
+			)
+		).toBe('--input data.csv --config /tmp/cfg.json --host host1')
+	})
+
+	it('still escapes a backtick in the literal text', () => {
+		expect(escapeTemplateBackticks('a ` b')).toBe('a \\` b')
+		expect(escapeTemplateBackticks('a ` ${x} ` b')).toBe('a \\` ${x} \\` b')
+	})
+
+	it('leaves an escaped interpolation as literal text', () => {
+		// `\\${...}` is escaped in the template source, so the backticks inside it are literal
+		// text and still need escaping.
+		expect(escapeTemplateBackticks('\\${foo `bar`}')).toBe('\\${foo \\`bar\\`}')
+		expect(unescapeTemplateBackticks('\\${foo \\`bar\\`}')).toBe('\\${foo `bar`}')
+		expect(
+			() => new Function('return `' + escapeTemplateBackticks('\\${foo `bar`}') + '`')
+		).not.toThrow()
+	})
+
+	// Braces, quotes, regex literals and comments all hide backticks and braces from anything
+	// short of a real lexer, which is why the parser decides.
+	it('handles text only a lexer can read correctly', () => {
+		const inputs = [
+			'${ x["}"] } `',
+			"${ f({ a: '`' }) } `",
+			"${ x.replace(/'/g, '') } `",
+			'${ /* ` */ x } `',
+			'{"match": ${/{/.test(flow_input.x)}, "literal": "`x`"}'
+		]
+		for (const v of inputs) {
+			expect(() => new Function('return `' + escapeTemplateBackticks(v) + '`')).not.toThrow()
+			expect(unescapeTemplateBackticks(escapeTemplateBackticks(v))).toBe(v)
+		}
+	})
+
+	// The failure that matters most is not a syntax error but literal text quietly becoming code:
+	// here the author's `+ flow_input.y +` must stay text rather than being evaluated.
+	it('never lets literal text escape into the expression', () => {
+		const v = '{"match": ${/{/.test(flow_input.x)}, "literal": "` + flow_input.y + `"}'
+		const evaluated = new Function('flow_input', 'return `' + escapeTemplateBackticks(v) + '`')({
+			x: 'x',
+			y: 'LEAKED'
+		})
+		expect(evaluated).not.toContain('LEAKED')
+		expect(evaluated).toContain('` + flow_input.y + `')
+	})
+
+	// An expression the old blanket rule broke — it escaped backticks inside `${...}`, which
+	// does not parse — comes back as the author typed it, instead of showing the backslashes
+	// and escaping them one deeper on every save.
+	it('heals an expression the old rule broke', () => {
+		const broken = '-p ${a}${b ? \\` --x ${c}\\` : ""}'
+		const clean = '-p ${a}${b ? ` --x ${c}` : ""}'
+		expect(unescapeTemplateBackticks(broken)).toBe(clean)
+		expect(escapeTemplateBackticks(clean)).toBe(clean)
+	})
+
+	// A text that already parses is left alone: an over-escaped legacy value and a backslash the
+	// author wrote are the same bytes, so healing on looks alone would drop a real character.
+	it('leaves an expression that already parses alone', () => {
+		const run = (body: string) => new Function('return `' + body + '`')()
+		for (const stored of ['${"\\`"}', '${"a\\\\`"}']) {
+			expect(unescapeTemplateBackticks(stored)).toBe(stored)
+			expect(run(escapeTemplateBackticks(unescapeTemplateBackticks(stored)))).toBe(run(stored))
+		}
+	})
+
+	// ...but a backtick escaped inside a nested template belongs there and must survive.
+	it('leaves an escaped backtick that is inside a nested template alone', () => {
+		const stored = '${cond ? `a\\`b` : ""}'
+		expect(unescapeTemplateBackticks(stored)).toBe(stored)
+	})
+
+	// Escapes the author wrote inside a nested template are not the old rule's doing, and
+	// stripping them changes what the expression means — here into chained tagged templates,
+	// which throw. Only a text whose backticks are *all* escaped came from the old rule.
+	it('leaves escapes that belong to a nested template alone', () => {
+		const run = (body: string) => new Function('flag', 'value', 'return `' + body + '`')(true, 'X')
+		for (const stored of ['${flag ? `\\`\\`${value}\\`\\`` : ""}', '${flag ? `a\\`b` : ""}']) {
+			expect(unescapeTemplateBackticks(stored)).toBe(stored)
+			expect(escapeTemplateBackticks(unescapeTemplateBackticks(stored))).toBe(stored)
+			expect(run(stored)).toBe(run(escapeTemplateBackticks(unescapeTemplateBackticks(stored))))
+		}
+	})
+
+	it('round-trips through unescapeTemplateBackticks', () => {
+		for (const v of [
+			nested,
+			'a ` b',
+			'${ x["}"] } `',
+			'plain',
+			'${a}${b}',
+			'\\${a}',
+			'${cond ? `a\\`b` : ""}'
+		]) {
+			expect(unescapeTemplateBackticks(escapeTemplateBackticks(v))).toBe(v)
+		}
+	})
+	// The guarantee that matters: opening a flow in the editor and saving it back must not change
+	// the stored expression, including for a value that only the all-or-nothing fallback can
+	// handle.
+	it('never rewrites the stored expression on a view/save cycle', () => {
+		const inputs = [
+			'{"match": ${/{/.test(flow_input.x)}, "literal": "`x`"}',
+			'${cond ? `a\\`b` : ""}',
+			"${ x.replace(/'/g, '') } `",
+			'a ` b',
+			'${ /* ` */ x } `'
+		]
+		for (const v of inputs) {
+			const stored = escapeTemplateBackticks(v)
+			expect(() => new Function('return `' + stored + '`')).not.toThrow()
+			expect(escapeTemplateBackticks(unescapeTemplateBackticks(stored))).toBe(stored)
+		}
+	})
+})
@@ -0,0 +1,59 @@
+import { parseExpressionAt } from 'acorn'
+
+/**
+ * Template mode stores what the author typed as a JS template literal, so the text is spliced
+ * between backticks. A backtick in the literal part has to be escaped or it ends the literal
+ * early — but one inside a `${...}` must not be, since a backslash is a syntax error in
+ * expression position and a nested template literal there is legitimate.
+ *
+ * Telling those apart means knowing where each `${...}` ends, which needs a real JS lexer:
+ * regex literals, comments and nested templates all hide braces and backticks from anything
+ * simpler. So rather than escaping selectively, ask the parser whether the text already reads as
+ * one template literal. If it does, it needs no escaping at all; if it does not, escape every
+ * backtick, which is what this did before nested templates were supported.
+ *
+ * Known limitation: a value mixing a bare literal backtick with a nested template cannot be
+ * expressed either way, and gets the all-or-nothing fallback. Escaping the literal one by hand
+ * makes the whole value parse and it is then kept verbatim.
+ */
+function isCompleteTemplateBody(text: string): boolean {
+	const source = '`' + text + '`'
+	try {
+		const node = parseExpressionAt(source, 0, { ecmaVersion: 'latest' })
+		// The type is what rejects a body that closes its own literal early: `` ` + evil() + ` ``
+		// parses, but as a concatenation, and would evaluate the author's literal text. The span
+		// rejects a body that stops short, like `` `a` x ``.
+		return node.type === 'TemplateLiteral' && node.start === 0 && node.end === source.length
+	} catch {
+		return false
+	}
+}
+
+/** Escape `text` so it can be wrapped in backticks and mean what the author typed. */
+export function escapeTemplateBackticks(text: string): string {
+	// No backtick means nothing to escape and nothing to decide, which is every ordinary value.
+	if (!text.includes('`')) {
+		return text
+	}
+	return isCompleteTemplateBody(text) ? text : text.replaceAll('`', '\\`')
+}
+
+/** Inverse of {@link escapeTemplateBackticks}, for turning an expression back into a template. */
+export function unescapeTemplateBackticks(text: string): string {
+	if (!text.includes('`')) {
+		return text
+	}
+	const unescaped = text.replaceAll('\\`', '`')
+	if (escapeTemplateBackticks(unescaped) === text) {
+		return unescaped
+	}
+	// Only an expression the old blanket rule *broke* is healed: it escaped backticks inside
+	// `${...}` too, which does not parse, while the unescaped form does. A text that already
+	// parses is left alone even if it looks over-escaped, because the two are indistinguishable
+	// from the text alone and guessing changes what the expression means — `${"a\\\\`"}` is a
+	// backslash the author wrote, not one the old rule added.
+	if (!isCompleteTemplateBody(text) && isCompleteTemplateBody(unescaped)) {
+		return unescaped
+	}
+	return text
+}