diff --git a/src/voice_transcriptor/services/job_manifest.py b/src/voice_transcriptor/services/job_manifest.py
new file mode 100644
index 0000000..f8271b4
--- /dev/null
+++ b/src/voice_transcriptor/services/job_manifest.py
@@ -0,0 +1,199 @@
+from __future__ import annotations
+
+import json
+from datetime import datetime, timezone
+from enum import StrEnum
+from pathlib import Path, PurePosixPath
+from typing import Iterable, Sequence
+
+
+class JobManifestError(RuntimeError):
+    pass
+
+
+class ChunkStatus(StrEnum):
+    PENDING = "pending"
+    PROCESSING = "processing"
+    COMPLETED = "completed"
+    FAILED = "failed"
+
+
+def _now() -> str:
+    return datetime.now(timezone.utc).isoformat()
+
+
+class JobManifestRepository:
+    def create(
+        self,
+        job_directory: Path,
+        source: dict,
+        settings: dict,
+        chunks: Sequence[dict],
+    ) -> dict:
+        job_directory = job_directory.resolve()
+        job_directory.mkdir(parents=True, exist_ok=True)
+        (job_directory / "chunks").mkdir(exist_ok=True)
+        timestamp = _now()
+        items = [self._new_chunk(item) for item in chunks]
+        manifest_path = job_directory / "manifest.json"
+        manifest = {
+            "schema_version": 2,
+            "job_id": job_directory.name,
+            "state": "preprocessing",
+            "source": dict(source),
+            "settings": dict(settings),
+            "created_at": timestamp,
+            "updated_at": timestamp,
+            "started_at": None,
+            "completed_at": None,
+            "chunks": items,
+            "completed_chunks": 0,
+            "total_chunks": len(items),
+            "error": None,
+        }
+        self.save(manifest_path, manifest)
+        return {**manifest, "manifest_path": str(manifest_path)}
+
+    def load(self, path: Path) -> dict:
+        try:
+            manifest = json.loads(path.read_text(encoding="utf-8"))
+        except (OSError, json.JSONDecodeError) as exc:
+            raise JobManifestError("Could not load the job manifest.") from exc
+        self._validate(manifest)
+        return manifest
+
+    def save(self, path: Path, manifest: dict) -> None:
+        self._validate(manifest)
+        manifest["updated_at"] = _now()
+        temporary = path.with_suffix(".tmp")
+        try:
+            temporary.write_text(json.dumps(manifest, ensure_ascii=False, indent=2), encoding="utf-8")
+            temporary.replace(path)
+        except OSError as exc:
+            raise JobManifestError("Could not save the job manifest.") from exc
+
+    def mark_processing(self, path: Path, index: int) -> dict:
+        manifest = self.load(path)
+        item = self._item(manifest, index)
+        if item["status"] == ChunkStatus.COMPLETED:
+            raise JobManifestError("A completed chunk cannot be processed again.")
+        item["status"] = ChunkStatus.PROCESSING
+        item["attempt_count"] += 1
+        item["last_error"] = None
+        if manifest["started_at"] is None:
+            manifest["started_at"] = _now()
+        manifest["state"] = "transcribing"
+        self.save(path, manifest)
+        return manifest
+
+    def mark_completed(self, path: Path, index: int, text: str) -> dict:
+        manifest = self.load(path)
+        item = self._item(manifest, index)
+        item["status"] = ChunkStatus.COMPLETED
+        item["transcript"] = text
+        item["last_error"] = None
+        item["completed_at"] = _now()
+        self._recount(manifest)
+        self.save(path, manifest)
+        return manifest
+
+    def mark_failed(self, path: Path, index: int, message: str) -> dict:
+        manifest = self.load(path)
+        item = self._item(manifest, index)
+        if item["status"] == ChunkStatus.COMPLETED:
+            raise JobManifestError("A completed chunk cannot be marked failed.")
+        item["status"] = ChunkStatus.FAILED
+        item["last_error"] = self._sanitize(message)
+        manifest["state"] = "failed"
+        manifest["error"] = item["last_error"]
+        self.save(path, manifest)
+        return manifest
+
+    def mark_job_state(self, path: Path, state: str, error: str | None = None) -> dict:
+        manifest = self.load(path)
+        manifest["state"] = state
+        manifest["error"] = self._sanitize(error) if error else None
+        if state == "completed":
+            manifest["completed_at"] = _now()
+        self.save(path, manifest)
+        return manifest
+
+    def recover_for_resume(self, path: Path) -> dict:
+        manifest = self.load(path)
+        for item in manifest["chunks"]:
+            if item["status"] in (ChunkStatus.PROCESSING, ChunkStatus.FAILED):
+                item["status"] = ChunkStatus.PENDING
+                item["last_error"] = None
+        manifest["state"] = "transcribing"
+        manifest["error"] = None
+        self._recount(manifest)
+        self.save(path, manifest)
+        return manifest
+
+    def reset_completed(self, path: Path, indexes: Iterable[int] | None = None) -> dict:
+        manifest = self.load(path)
+        selected = set(indexes) if indexes is not None else {item["index"] for item in manifest["chunks"]}
+        for item in manifest["chunks"]:
+            if item["index"] in selected and item["status"] == ChunkStatus.COMPLETED:
+                item.update(status=ChunkStatus.PENDING, transcript=None, completed_at=None, last_error=None)
+        self._recount(manifest)
+        self.save(path, manifest)
+        return manifest
+
+    def assemble_transcript(self, manifest_path: Path) -> Path:
+        manifest = self.load(manifest_path)
+        texts = [
+            item["transcript"]
+            for item in sorted(manifest["chunks"], key=lambda value: value["index"])
+            if item["status"] == ChunkStatus.COMPLETED and item["transcript"] is not None
+        ]
+        target = manifest_path.parent / "transcript.txt"
+        temporary = target.with_suffix(".tmp")
+        temporary.write_text("".join(f"{text}\n" for text in texts), encoding="utf-8")
+        temporary.replace(target)
+        return target
+
+    @staticmethod
+    def _new_chunk(source: dict) -> dict:
+        relative = PurePosixPath(str(source.get("path", "")))
+        if relative.is_absolute() or ".." in relative.parts or not relative.parts or relative.parts[0] != "chunks":
+            raise JobManifestError("Invalid chunk path in job manifest.")
+        return {
+            **source,
+            "path": relative.as_posix(),
+            "status": ChunkStatus.PENDING,
+            "attempt_count": 0,
+            "transcript": None,
+            "last_error": None,
+            "completed_at": None,
+        }
+
+    @staticmethod
+    def _validate(manifest: object) -> None:
+        if not isinstance(manifest, dict) or manifest.get("schema_version") != 2:
+            raise JobManifestError("Unsupported job manifest schema.")
+        chunks = manifest.get("chunks")
+        if not isinstance(chunks, list):
+            raise JobManifestError("Invalid chunks in job manifest.")
+        for item in chunks:
+            if not isinstance(item, dict):
+                raise JobManifestError("Invalid chunk in job manifest.")
+            relative = PurePosixPath(str(item.get("path", "")))
+            if relative.is_absolute() or ".." in relative.parts or not relative.parts or relative.parts[0] != "chunks":
+                raise JobManifestError("Invalid chunk path in job manifest.")
+
+    @staticmethod
+    def _item(manifest: dict, index: int) -> dict:
+        for item in manifest["chunks"]:
+            if item.get("index") == index:
+                return item
+        raise JobManifestError("Unknown chunk index.")
+
+    @staticmethod
+    def _recount(manifest: dict) -> None:
+        manifest["completed_chunks"] = sum(item["status"] == ChunkStatus.COMPLETED for item in manifest["chunks"])
+
+    @staticmethod
+    def _sanitize(message: str) -> str:
+        value = str(message).replace("\r", " ").replace("\n", " ")
+        return value[:500]
diff --git a/tests/test_job_manifest.py b/tests/test_job_manifest.py
new file mode 100644
index 0000000..5931221
--- /dev/null
+++ b/tests/test_job_manifest.py
@@ -0,0 +1,113 @@
+import json
+from pathlib import Path
+
+import pytest
+
+from voice_transcriptor.services.job_manifest import JobManifestError, JobManifestRepository
+
+
+def chunks() -> list[dict]:
+    return [
+        {
+            "index": 0,
+            "path": "chunks/chunk-00000.m4a",
+            "source_start_seconds": "0",
+            "source_end_seconds": "900.125",
+            "duration_seconds": "900.125",
+        },
+        {
+            "index": 1,
+            "path": "chunks/chunk-00001.m4a",
+            "source_start_seconds": "885.125",
+            "source_end_seconds": "1000.5",
+            "duration_seconds": "115.375",
+        },
+    ]
+
+
+def create_manifest(tmp_path: Path) -> tuple[JobManifestRepository, Path]:
+    job = tmp_path / "job"
+    repository = JobManifestRepository()
+    manifest = repository.create(
+        job,
+        source={"path": str(tmp_path / "source.mp3"), "size_bytes": 10},
+        settings={"model": "gpt-transcribe", "language": "pt-BR"},
+        chunks=chunks(),
+    )
+    return repository, Path(manifest["manifest_path"])
+
+
+def test_create_persists_schema_timing_and_pending_statuses(tmp_path: Path) -> None:
+    repository, path = create_manifest(tmp_path)
+
+    manifest = repository.load(path)
+
+    assert manifest["schema_version"] == 2
+    assert manifest["state"] == "preprocessing"
+    assert manifest["completed_chunks"] == 0
+    assert manifest["total_chunks"] == 2
+    assert [item["status"] for item in manifest["chunks"]] == ["pending", "pending"]
+    assert manifest["chunks"][1]["source_start_seconds"] == "885.125"
+    assert not path.with_suffix(".tmp").exists()
+
+
+def test_create_rejects_chunk_path_outside_job(tmp_path: Path) -> None:
+    invalid = chunks()
+    invalid[0]["path"] = "../secret.m4a"
+
+    with pytest.raises(JobManifestError, match="chunk path"):
+        JobManifestRepository().create(tmp_path / "job", {}, {}, invalid)
+
+
+def test_completed_chunk_is_written_immediately_and_cannot_be_reprocessed(tmp_path: Path) -> None:
+    repository, path = create_manifest(tmp_path)
+
+    repository.mark_processing(path, 0)
+    repository.mark_completed(path, 0, "Primeiro trecho")
+    on_disk = json.loads(path.read_text(encoding="utf-8"))
+
+    assert on_disk["chunks"][0]["status"] == "completed"
+    assert on_disk["chunks"][0]["transcript"] == "Primeiro trecho"
+    assert on_disk["completed_chunks"] == 1
+    with pytest.raises(JobManifestError, match="completed"):
+        repository.mark_processing(path, 0)
+
+
+def test_resume_recovers_processing_and_failed_but_preserves_completed(tmp_path: Path) -> None:
+    repository, path = create_manifest(tmp_path)
+    repository.mark_processing(path, 0)
+    repository.mark_completed(path, 0, "Feito")
+    repository.mark_processing(path, 1)
+    repository.mark_failed(path, 1, "temporary failure")
+
+    manifest = repository.recover_for_resume(path)
+
+    assert manifest["chunks"][0]["status"] == "completed"
+    assert manifest["chunks"][0]["transcript"] == "Feito"
+    assert manifest["chunks"][1]["status"] == "pending"
+    assert manifest["chunks"][1]["last_error"] is None
+
+
+def test_assemble_transcript_uses_only_completed_chunks_in_index_order(tmp_path: Path) -> None:
+    repository, path = create_manifest(tmp_path)
+    repository.mark_processing(path, 1)
+    repository.mark_completed(path, 1, "Segundo")
+    repository.mark_processing(path, 0)
+    repository.mark_completed(path, 0, "Primeiro")
+
+    transcript_path = repository.assemble_transcript(path)
+
+    assert transcript_path.read_text(encoding="utf-8") == "Primeiro\nSegundo\n"
+    assert repository.load(path)["chunks"][1]["source_end_seconds"] == "1000.5"
+
+
+def test_explicit_reset_is_required_to_clear_completed_work(tmp_path: Path) -> None:
+    repository, path = create_manifest(tmp_path)
+    repository.mark_processing(path, 0)
+    repository.mark_completed(path, 0, "Feito")
+
+    repository.reset_completed(path, indexes=[0])
+
+    item = repository.load(path)["chunks"][0]
+    assert item["status"] == "pending"
+    assert item["transcript"] is None