diff --git a/coordinator/api/requests.http b/coordinator/api/requests.http
index 303c3a3..6c50a59 100644
--- a/coordinator/api/requests.http
+++ b/coordinator/api/requests.http
@@ -34,6 +34,41 @@ Content-Type: application/json
 
 @workerId = {{register.response.body.worker_id}}
 
+### 0b. Upload a dataset — the coordinator splits it into shard tasks (201)
+# Text fields first, the file part last (it is streamed, not buffered).
+# @name uploadJob
+POST {{host}}/jobs/upload
+Authorization: Bearer {{token}}
+Content-Type: multipart/form-data; boundary=----scimesh
+
+------scimesh
+Content-Disposition: form-data; name="workload"
+
+similarity_search
+------scimesh
+Content-Disposition: form-data; name="parameters"
+
+{"top_k":10}
+------scimesh
+Content-Disposition: form-data; name="chunk_rows"
+
+2
+------scimesh
+Content-Disposition: form-data; name="file"; filename="chembl.tsv"
+Content-Type: text/tab-separated-values
+
+id	smiles
+A	CC
+B	CCC
+C	CCCC
+D	CCCCC
+------scimesh--
+
+### Download a task's input shard (200) — taskId must be a shard task from an
+### uploaded job (claim one first; its input.uri is /tasks/{id}/input).
+GET {{host}}/tasks/{{taskId}}/input
+Authorization: Bearer {{token}}
+
 ### 1. Create a job and its chunks (201)
 # The coordinator splits the submission into one task per chunk, transactionally.
 # @name createJob
diff --git a/coordinator/cmd/coordinator/main.go b/coordinator/cmd/coordinator/main.go
index 95481fc..767ebeb 100644
--- a/coordinator/cmd/coordinator/main.go
+++ b/coordinator/cmd/coordinator/main.go
@@ -70,6 +70,7 @@ func run() error {
 	useCases := httptransport.UseCases{
 		RegisterWorker:   usecase.NewRegisterWorker(workerRepo, clk),
 		CreateJob:        usecase.NewCreateJob(jobRepo, taskRepo, tx, clk),
+		SubmitDataset:    usecase.NewSubmitDataset(blobStore, artifactRepo, jobRepo, taskRepo, tx, clk),
 		ClaimTask:        usecase.NewClaimTask(taskRepo, clk, cfg.LeaseDuration),
 		RenewLease:       usecase.NewRenewLease(taskRepo, tx, clk, cfg.LeaseDuration),
 		CompleteTask:     usecase.NewCompleteTask(taskRepo, jobRepo, artifactRepo, tx, clk),
@@ -77,6 +78,7 @@ func run() error {
 		GetJobStatus:     usecase.NewGetJobStatus(jobRepo, taskRepo),
 		UploadArtifact:   usecase.NewUploadArtifact(taskRepo, artifactRepo, blobStore, clk),
 		DownloadArtifact: usecase.NewDownloadArtifact(artifactRepo, blobStore),
+		GetTaskInput:     usecase.NewGetTaskInput(taskRepo, artifactRepo, blobStore),
 	}
 
 	// Background workers are tracked so shutdown can wait for them. Without
diff --git a/coordinator/internal/chunk/tsv.go b/coordinator/internal/chunk/tsv.go
new file mode 100644
index 0000000..6b968eb
--- /dev/null
+++ b/coordinator/internal/chunk/tsv.go
@@ -0,0 +1,92 @@
+// Package chunk splits a tabular input into deterministic shards. It is generic
+// row splitting only — no workload semantics (SMILES, top-k) live here.
+package chunk
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+)
+
+// ErrNoRows is returned when the input has a header but no data rows: a job with
+// zero tasks could never complete, so it is rejected at the source.
+var ErrNoRows = fmt.Errorf("input has no data rows")
+
+// SplitTSV reads a header-plus-rows text stream and cuts it into shards of at
+// most rowsPerShard data rows. Every shard repeats the header, so a worker can
+// parse its shard in isolation. emit is called once per shard, in order, with a
+// reader over that shard's bytes; the reader is valid only for the duration of
+// the call.
+//
+// Splitting is deterministic: the same input and rowsPerShard always produce the
+// same shards, byte for byte — which is what lets chunk_index refer to a stable
+// piece and makes a re-run reproducible.
+//
+// Only one shard is buffered at a time, so memory is bounded by shard size (a
+// worker-sized slice of the data), not by the size of the whole dataset.
+func SplitTSV(r io.Reader, rowsPerShard int, emit func(index int, shard io.Reader) error) error {
+	if rowsPerShard <= 0 {
+		return fmt.Errorf("rowsPerShard must be positive, got %d", rowsPerShard)
+	}
+
+	sc := bufio.NewScanner(r)
+	// Allow long lines: a SMILES row can be far wider than bufio's 64 KB default.
+	sc.Buffer(make([]byte, 0, 64*1024), 8*1024*1024)
+
+	if !sc.Scan() {
+		if err := sc.Err(); err != nil {
+			return fmt.Errorf("read header: %w", err)
+		}
+		return ErrNoRows // completely empty input
+	}
+	header := append([]byte(nil), sc.Bytes()...)
+
+	var (
+		buf   bytes.Buffer
+		rows  int
+		index int
+	)
+
+	// flush emits the buffered shard and resets for the next one.
+	flush := func() error {
+		if err := emit(index, bytes.NewReader(buf.Bytes())); err != nil {
+			return err
+		}
+		index++
+		buf.Reset()
+		rows = 0
+		return nil
+	}
+
+	for sc.Scan() {
+		if rows == 0 {
+			buf.Write(header)
+			buf.WriteByte('\n')
+		}
+		buf.Write(sc.Bytes())
+		buf.WriteByte('\n')
+		rows++
+
+		if rows == rowsPerShard {
+			if err := flush(); err != nil {
+				return err
+			}
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return fmt.Errorf("read rows: %w", err)
+	}
+
+	// A partial final shard still has to go out.
+	if rows > 0 {
+		if err := flush(); err != nil {
+			return err
+		}
+	}
+
+	if index == 0 {
+		return ErrNoRows // header only, no data
+	}
+	return nil
+}
diff --git a/coordinator/internal/chunk/tsv_test.go b/coordinator/internal/chunk/tsv_test.go
new file mode 100644
index 0000000..ba12917
--- /dev/null
+++ b/coordinator/internal/chunk/tsv_test.go
@@ -0,0 +1,117 @@
+package chunk
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+	"testing"
+)
+
+// collect runs SplitTSV and returns every shard as a string.
+func collect(t *testing.T, input string, rowsPerShard int) []string {
+	t.Helper()
+	var shards []string
+	err := SplitTSV(strings.NewReader(input), rowsPerShard, func(index int, shard io.Reader) error {
+		b, _ := io.ReadAll(shard)
+		if index != len(shards) {
+			t.Fatalf("emit index = %d, want %d (out of order)", index, len(shards))
+		}
+		shards = append(shards, string(b))
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("SplitTSV: %v", err)
+	}
+	return shards
+}
+
+func TestSplitCountsShardsAndRepeatsHeader(t *testing.T) {
+	input := "id\tsmiles\nA\tCC\nB\tCCC\nC\tCCCC\nD\tCCCCC\nE\tCCCCCC\n"
+	shards := collect(t, input, 2)
+
+	if len(shards) != 3 { // 5 rows / 2 per shard = ceil = 3
+		t.Fatalf("got %d shards, want 3", len(shards))
+	}
+	for i, s := range shards {
+		if !strings.HasPrefix(s, "id\tsmiles\n") {
+			t.Errorf("shard %d missing header: %q", i, s)
+		}
+	}
+	if shards[0] != "id\tsmiles\nA\tCC\nB\tCCC\n" {
+		t.Errorf("shard 0 = %q", shards[0])
+	}
+	if shards[2] != "id\tsmiles\nE\tCCCCCC\n" { // partial final shard
+		t.Errorf("shard 2 = %q", shards[2])
+	}
+}
+
+func TestSplitExactMultipleHasNoEmptyTrailingShard(t *testing.T) {
+	input := "h\nr1\nr2\nr3\nr4\n"
+	shards := collect(t, input, 2)
+	if len(shards) != 2 { // exactly 4/2, no empty third shard
+		t.Fatalf("got %d shards, want 2", len(shards))
+	}
+}
+
+func TestSplitIsDeterministic(t *testing.T) {
+	input := "h\n" + strings.Repeat("row\n", 100)
+	a := collect(t, input, 7)
+	b := collect(t, input, 7)
+	if fmt.Sprint(a) != fmt.Sprint(b) {
+		t.Error("two runs produced different shards")
+	}
+}
+
+func TestSplitRejectsHeaderOnly(t *testing.T) {
+	err := SplitTSV(strings.NewReader("id\tsmiles\n"), 10, func(int, io.Reader) error { return nil })
+	if !errors.Is(err, ErrNoRows) {
+		t.Errorf("err = %v, want ErrNoRows", err)
+	}
+}
+
+func TestSplitRejectsEmptyInput(t *testing.T) {
+	err := SplitTSV(strings.NewReader(""), 10, func(int, io.Reader) error { return nil })
+	if !errors.Is(err, ErrNoRows) {
+		t.Errorf("err = %v, want ErrNoRows", err)
+	}
+}
+
+func TestSplitRejectsNonPositiveSize(t *testing.T) {
+	err := SplitTSV(strings.NewReader("h\nr\n"), 0, func(int, io.Reader) error { return nil })
+	if err == nil {
+		t.Error("expected an error for rowsPerShard = 0")
+	}
+}
+
+func TestSplitPropagatesEmitError(t *testing.T) {
+	boom := errors.New("boom")
+	err := SplitTSV(strings.NewReader("h\nr1\nr2\n"), 1, func(int, io.Reader) error { return boom })
+	if !errors.Is(err, boom) {
+		t.Errorf("err = %v, want boom", err)
+	}
+}
+
+func TestSplitSingleShardWhenSizeExceedsRows(t *testing.T) {
+	shards := collect(t, "h\nr1\nr2\n", 100)
+	if len(shards) != 1 {
+		t.Fatalf("got %d shards, want 1", len(shards))
+	}
+	if shards[0] != "h\nr1\nr2\n" {
+		t.Errorf("shard 0 = %q", shards[0])
+	}
+}
+
+// The scanned bytes are reused by bufio; the shard buffer must copy them, or a
+// later row would corrupt an earlier one. This guards that copy.
+func TestSplitDoesNotAliasScannerBuffer(t *testing.T) {
+	var got bytes.Buffer
+	_ = SplitTSV(strings.NewReader("h\naaaa\nbbbb\n"), 2, func(_ int, shard io.Reader) error {
+		_, _ = io.Copy(&got, shard)
+		return nil
+	})
+	if want := "h\naaaa\nbbbb\n"; got.String() != want {
+		t.Errorf("got %q, want %q", got.String(), want)
+	}
+}
diff --git a/coordinator/internal/domain/job.go b/coordinator/internal/domain/job.go
index b6e9f4a..0aa4827 100644
--- a/coordinator/internal/domain/job.go
+++ b/coordinator/internal/domain/job.go
@@ -18,13 +18,31 @@ const (
 
 // Job is one user submission that fans out into one or more tasks.
 type Job struct {
-	ID          uuid.UUID
-	Workload    string
-	InputURI    string
-	Parameters  map[string]any
-	Status      JobStatus
-	CreatedAt   time.Time
-	CompletedAt *time.Time
+	ID              uuid.UUID
+	Workload        string
+	InputURI        string     // external input URI; empty for uploaded datasets
+	InputArtifactID *uuid.UUID // uploaded input artifact; nil for URI submissions
+	Parameters      map[string]any
+	Status          JobStatus
+	CreatedAt       time.Time
+	CompletedAt     *time.Time
+}
+
+// NewUploadedJob builds a job whose input was uploaded to the coordinator. The
+// job's id is generated here so the input artifact can reference it; the reverse
+// link (jobs.input_artifact_id) is left unset — the input is found via the
+// artifact's job_id — which also sidesteps the circular job↔artifact FK.
+func NewUploadedJob(workload string, params map[string]any, now time.Time) (*Job, error) {
+	if workload == "" {
+		return nil, ErrInvalidInput
+	}
+	return &Job{
+		ID:         uuid.New(),
+		Workload:   workload,
+		Parameters: params,
+		Status:     JobPending,
+		CreatedAt:  now,
+	}, nil
 }
 
 // ChunkSpec describes one piece a job is split into. Callers build these from
diff --git a/coordinator/internal/domain/task.go b/coordinator/internal/domain/task.go
index 87fc555..8908e44 100644
--- a/coordinator/internal/domain/task.go
+++ b/coordinator/internal/domain/task.go
@@ -32,7 +32,8 @@ type Task struct {
 	JobID            uuid.UUID
 	ChunkIndex       int
 	Workload         string
-	InputURI         string
+	InputURI         string     // external input URI; empty for uploaded shards
+	InputArtifactID  *uuid.UUID // coordinator-stored shard; nil for URI inputs
 	InputSHA256      string
 	Parameters       map[string]any
 	Status           TaskStatus
@@ -81,6 +82,33 @@ func NewTask(jobID uuid.UUID, chunkIndex int, workload, inputURI, inputSHA256 st
 	}, nil
 }
 
+// NewShardTask builds a pending task whose input is a coordinator-stored shard
+// artifact rather than an external URI. The worker fetches it from the
+// coordinator, so no InputURI is set — inputSHA256 is the shard's checksum.
+func NewShardTask(jobID uuid.UUID, chunkIndex int, workload string, inputArtifactID uuid.UUID,
+	inputSHA256 string, params map[string]any, maxAttempts int, now time.Time) (*Task, error) {
+
+	if inputArtifactID == uuid.Nil || inputSHA256 == "" || chunkIndex < 0 {
+		return nil, ErrInvalidInput
+	}
+	if maxAttempts <= 0 {
+		maxAttempts = DefaultMaxAttempts
+	}
+	return &Task{
+		ID:              uuid.New(),
+		JobID:           jobID,
+		ChunkIndex:      chunkIndex,
+		Workload:        workload,
+		InputArtifactID: &inputArtifactID,
+		InputSHA256:     inputSHA256,
+		Parameters:      params,
+		Status:          TaskPending,
+		Attempt:         0,
+		MaxAttempts:     maxAttempts,
+		CreatedAt:       now,
+	}, nil
+}
+
 // DefaultMaxAttempts applies when a task does not specify its own ceiling.
 const DefaultMaxAttempts = 3
 
@@ -96,14 +124,15 @@ func (t *Task) IsLeaseHeldBy(worker string, attempt int) bool {
 // everything needed to execute, nothing it has no business seeing.
 func (t *Task) AsClaimed() ClaimedTask {
 	ct := ClaimedTask{
-		TaskID:      t.ID,
-		JobID:       t.JobID,
-		ChunkIndex:  t.ChunkIndex,
-		Workload:    t.Workload,
-		InputURI:    t.InputURI,
-		InputSHA256: t.InputSHA256,
-		Parameters:  t.Parameters,
-		Attempt:     t.Attempt,
+		TaskID:          t.ID,
+		JobID:           t.JobID,
+		ChunkIndex:      t.ChunkIndex,
+		Workload:        t.Workload,
+		InputURI:        t.InputURI,
+		InputArtifactID: t.InputArtifactID,
+		InputSHA256:     t.InputSHA256,
+		Parameters:      t.Parameters,
+		Attempt:         t.Attempt,
 	}
 	if t.LeaseOwner != nil {
 		ct.LeaseOwner = *t.LeaseOwner
@@ -217,18 +246,21 @@ func (t *Task) ExpireLease(now time.Time) {
 	t.CompletedAt = &now
 }
 
-// ClaimedTask is the worker-facing projection of a leased task.
+// ClaimedTask is the worker-facing projection of a leased task. Input is either
+// an external URI or a coordinator-stored shard (InputArtifactID set); the
+// transport turns the latter into a coordinator download URL.
 type ClaimedTask struct {
-	TaskID         uuid.UUID
-	JobID          uuid.UUID
-	ChunkIndex     int
-	Workload       string
-	InputURI       string
-	InputSHA256    string
-	Parameters     map[string]any
-	Attempt        int
-	LeaseOwner     string
-	LeaseExpiresAt time.Time
+	TaskID          uuid.UUID
+	JobID           uuid.UUID
+	ChunkIndex      int
+	Workload        string
+	InputURI        string
+	InputArtifactID *uuid.UUID
+	InputSHA256     string
+	Parameters      map[string]any
+	Attempt         int
+	LeaseOwner      string
+	LeaseExpiresAt  time.Time
 }
 
 // ResultManifest is a completed task's output, ordered for the stitcher. It
diff --git a/coordinator/internal/infra/logging.go b/coordinator/internal/infra/logging.go
index 4d12e61..b5f49e3 100644
--- a/coordinator/internal/infra/logging.go
+++ b/coordinator/internal/infra/logging.go
@@ -29,7 +29,7 @@ func NewLogger(cfg Config) (*slog.Logger, io.Closer, error) {
 	)
 
 	if cfg.LogFile != "" {
-		if err := os.MkdirAll(filepath.Dir(cfg.LogFile), 0o755); err != nil {
+		if err := os.MkdirAll(filepath.Dir(cfg.LogFile), 0o750); err != nil {
 			return nil, nil, fmt.Errorf("create log directory: %w", err)
 		}
 		rotator := &lumberjack.Logger{
diff --git a/coordinator/internal/storage/blob/store.go b/coordinator/internal/storage/blob/store.go
index 7c20eac..db98600 100644
--- a/coordinator/internal/storage/blob/store.go
+++ b/coordinator/internal/storage/blob/store.go
@@ -28,7 +28,7 @@ var _ usecase.BlobStore = (*FSStore)(nil)
 // rename is only atomic within one filesystem.
 func NewFSStore(dir string) (*FSStore, error) {
 	staging := filepath.Join(dir, ".staging")
-	if err := os.MkdirAll(staging, 0o755); err != nil {
+	if err := os.MkdirAll(staging, 0o750); err != nil {
 		return nil, fmt.Errorf("create blob dirs: %w", err)
 	}
 	return &FSStore{dir: dir, staging: staging}, nil
@@ -85,7 +85,9 @@ func (s *FSStore) Open(ctx context.Context, key string) (io.ReadCloser, error) {
 	if err := checkKey(key); err != nil {
 		return nil, err
 	}
-	f, err := os.Open(filepath.Join(s.dir, key))
+	// checkKey has rejected any traversal, so the joined path stays under s.dir.
+	f, err := os.Open(filepath.Join(s.dir, key)) //nolint:gosec // key validated by checkKey
+
 	if err != nil {
 		return nil, err
 	}
diff --git a/coordinator/internal/storage/postgres/task_repo.go b/coordinator/internal/storage/postgres/task_repo.go
index d34f122..827ab77 100644
--- a/coordinator/internal/storage/postgres/task_repo.go
+++ b/coordinator/internal/storage/postgres/task_repo.go
@@ -30,7 +30,7 @@ var _ usecase.TaskRepository = (*TaskRepo)(nil)
 // Every query that returns a task selects exactly this list, in this order —
 // three hand-written column lists would drift apart within a week.
 var taskColumns = []string{
-	"id", "job_id", "chunk_index", "workload", "input_uri", "input_sha256",
+	"id", "job_id", "chunk_index", "workload", "input_uri", "input_artifact_id", "input_sha256",
 	"parameters", "status", "attempt", "max_attempts", "lease_owner", "lease_expires_at",
 	"result_artifact_id", "metrics", "error_code", "error_message",
 	"created_at", "started_at", "completed_at", "version",
@@ -49,9 +49,12 @@ func scanTask(row pgx.Row) (*domain.Task, error) {
 	var (
 		t      domain.Task
 		status string
+		// input_uri is nullable now (uploaded shards have none), so it cannot
+		// scan straight into a string; NULL becomes the empty InputURI.
+		inputURI *string
 	)
 	err := row.Scan(
-		&t.ID, &t.JobID, &t.ChunkIndex, &t.Workload, &t.InputURI, &t.InputSHA256,
+		&t.ID, &t.JobID, &t.ChunkIndex, &t.Workload, &inputURI, &t.InputArtifactID, &t.InputSHA256,
 		&t.Parameters, &status, &t.Attempt, &t.MaxAttempts, &t.LeaseOwner, &t.LeaseExpiresAt,
 		&t.ResultArtifactID, &t.Metrics, &t.ErrorCode, &t.ErrorMessage,
 		&t.CreatedAt, &t.StartedAt, &t.CompletedAt, &t.Version,
@@ -59,6 +62,9 @@ func scanTask(row pgx.Row) (*domain.Task, error) {
 	if err != nil {
 		return nil, err
 	}
+	if inputURI != nil {
+		t.InputURI = *inputURI
+	}
 	t.Status = domain.TaskStatus(status)
 	return &t, nil
 }
@@ -206,10 +212,12 @@ func (r *TaskRepo) InsertBatch(ctx context.Context, tasks []*domain.Task) error
 	batch := &pgx.Batch{}
 	for _, t := range tasks {
 		sql, args, err := psql.Insert("tasks").
-			Columns("id", "job_id", "chunk_index", "workload", "input_uri", "input_sha256",
-				"parameters", "status", "attempt", "max_attempts", "created_at", "version").
-			Values(t.ID, t.JobID, t.ChunkIndex, t.Workload, t.InputURI, t.InputSHA256,
-				jsonbOrEmpty(t.Parameters), string(t.Status), t.Attempt, t.MaxAttempts, t.CreatedAt, t.Version).
+			Columns("id", "job_id", "chunk_index", "workload", "input_uri", "input_artifact_id",
+				"input_sha256", "parameters", "status", "attempt", "max_attempts", "created_at", "version").
+			// input_uri is stored NULL (not "") when empty, so the ck_tasks_has_input
+			// check actually bites: a task with neither a URI nor an artifact fails.
+			Values(t.ID, t.JobID, t.ChunkIndex, t.Workload, nullIfEmpty(t.InputURI), t.InputArtifactID,
+				t.InputSHA256, jsonbOrEmpty(t.Parameters), string(t.Status), t.Attempt, t.MaxAttempts, t.CreatedAt, t.Version).
 			ToSql()
 		if err != nil {
 			return err
diff --git a/coordinator/internal/storage/postgres/tx.go b/coordinator/internal/storage/postgres/tx.go
index 4b70e17..38adaa7 100644
--- a/coordinator/internal/storage/postgres/tx.go
+++ b/coordinator/internal/storage/postgres/tx.go
@@ -84,6 +84,15 @@ func jsonbOrEmpty(m map[string]any) map[string]any {
 	return m
 }
 
+// nullIfEmpty maps "" to a SQL NULL, so an absent optional string is stored as
+// NULL rather than an empty string that would defeat a NOT-NULL-or check.
+func nullIfEmpty(s string) any {
+	if s == "" {
+		return nil
+	}
+	return s
+}
+
 // conn returns the transaction bound to ctx, or the pool when there is none.
 func conn(ctx context.Context, pool *pgxpool.Pool) querier {
 	if tx, ok := ctx.Value(txKey{}).(pgx.Tx); ok {
diff --git a/coordinator/internal/transport/http/dto.go b/coordinator/internal/transport/http/dto.go
index 6e014a3..c652b25 100644
--- a/coordinator/internal/transport/http/dto.go
+++ b/coordinator/internal/transport/http/dto.go
@@ -88,18 +88,28 @@ type taskResponse struct {
 	Status string    `json:"status"`
 }
 
+type inputRef struct {
+	URI    string `json:"uri"`
+	SHA256 string `json:"sha256"`
+}
+
 type claimedTaskResponse struct {
 	TaskID         uuid.UUID      `json:"task_id"`
 	JobID          uuid.UUID      `json:"job_id"`
 	ChunkIndex     int            `json:"chunk_index"`
 	Workload       string         `json:"workload"`
-	InputURI       string         `json:"input_uri"`
-	InputSHA256    string         `json:"input_sha256"`
+	Input          inputRef       `json:"input"`
 	Parameters     map[string]any `json:"parameters"`
 	Attempt        int            `json:"attempt"`
 	LeaseExpiresAt time.Time      `json:"lease_expires_at"`
 }
 
+type uploadJobResponse struct {
+	JobID           uuid.UUID `json:"job_id"`
+	TaskCount       int       `json:"task_count"`
+	InputArtifactID uuid.UUID `json:"input_artifact_id"`
+}
+
 type jobProgressResponse struct {
 	ID      uuid.UUID `json:"id"`
 	Status  string    `json:"status"`
@@ -123,13 +133,18 @@ type errorResponse struct {
 }
 
 func toClaimedTaskResponse(c domain.ClaimedTask) claimedTaskResponse {
+	// A shard's input lives in the coordinator; hand the worker a URL to fetch
+	// it from. A URI-based task keeps its external URI.
+	uri := c.InputURI
+	if c.InputArtifactID != nil {
+		uri = "/tasks/" + c.TaskID.String() + "/input"
+	}
 	return claimedTaskResponse{
 		TaskID:         c.TaskID,
 		JobID:          c.JobID,
 		ChunkIndex:     c.ChunkIndex,
 		Workload:       c.Workload,
-		InputURI:       c.InputURI,
-		InputSHA256:    c.InputSHA256,
+		Input:          inputRef{URI: uri, SHA256: c.InputSHA256},
 		Parameters:     c.Parameters,
 		Attempt:        c.Attempt,
 		LeaseExpiresAt: c.LeaseExpiresAt,
diff --git a/coordinator/internal/transport/http/handlers.go b/coordinator/internal/transport/http/handlers.go
index d622e0f..1165105 100644
--- a/coordinator/internal/transport/http/handlers.go
+++ b/coordinator/internal/transport/http/handlers.go
@@ -2,10 +2,13 @@ package http
 
 import (
 	"context"
+	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
 	"strconv"
+	"strings"
 
 	"github.com/google/uuid"
 
@@ -175,6 +178,107 @@ func (s *Server) handleFailure(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, taskResponse{ID: task.ID, JobID: task.JobID, Status: string(task.Status)})
 }
 
+// defaultChunkRows is the shard size used when a request omits chunk_rows.
+const defaultChunkRows = 1000
+
+// handleUploadDataset accepts a multipart submission — the dataset file plus the
+// workload/parameters/chunk_rows fields — and hands the file, streamed, to the
+// chunker. The text fields MUST precede the file part: the file is streamed, not
+// buffered, so by the time it arrives the other fields are already parsed.
+func (s *Server) handleUploadDataset(w http.ResponseWriter, r *http.Request) {
+	mr, err := r.MultipartReader()
+	if err != nil {
+		s.writeError(w, r, domain.ErrInvalidInput)
+		return
+	}
+
+	var (
+		workload   string
+		params     map[string]any
+		rows       = defaultChunkRows
+		result     usecase.SubmitDatasetResult
+		gotDataset bool
+	)
+
+	for {
+		part, err := mr.NextPart()
+		if errors.Is(err, io.EOF) {
+			break
+		}
+		if err != nil {
+			s.writeError(w, r, domain.ErrInvalidInput)
+			return
+		}
+
+		switch part.FormName() {
+		case "workload":
+			b, _ := io.ReadAll(io.LimitReader(part, 1<<10))
+			workload = strings.TrimSpace(string(b))
+		case "parameters":
+			b, _ := io.ReadAll(io.LimitReader(part, 1<<16))
+			if len(b) > 0 {
+				if err := json.Unmarshal(b, &params); err != nil {
+					s.writeError(w, r, domain.ErrInvalidInput)
+					return
+				}
+			}
+		case "chunk_rows":
+			b, _ := io.ReadAll(io.LimitReader(part, 32))
+			if n, err := strconv.Atoi(strings.TrimSpace(string(b))); err == nil {
+				rows = n
+			}
+		case "file", "dataset":
+			filename := part.FileName()
+			if filename == "" {
+				filename = "dataset"
+			}
+			result, err = s.uc.SubmitDataset.Execute(r.Context(), usecase.SubmitDatasetInput{
+				Workload:     workload,
+				Parameters:   params,
+				RowsPerShard: rows,
+				Filename:     filename,
+				ContentType:  part.Header.Get("Content-Type"),
+				Body:         part,
+			})
+			if err != nil {
+				s.writeError(w, r, err)
+				return
+			}
+			gotDataset = true
+		}
+		_ = part.Close()
+	}
+
+	if !gotDataset {
+		s.writeError(w, r, domain.ErrInvalidInput) // no file part
+		return
+	}
+	writeJSON(w, http.StatusCreated, uploadJobResponse{
+		JobID:           result.JobID,
+		TaskCount:       result.TaskCount,
+		InputArtifactID: result.InputArtifactID,
+	})
+}
+
+// handleGetTaskInput streams a task's input shard back to the worker.
+func (s *Server) handleGetTaskInput(w http.ResponseWriter, r *http.Request) {
+	taskID, ok := s.pathUUID(w, r, "task_id")
+	if !ok {
+		return
+	}
+	art, body, err := s.uc.GetTaskInput.Execute(r.Context(), taskID)
+	if err != nil {
+		s.writeError(w, r, err)
+		return
+	}
+	defer func() { _ = body.Close() }()
+
+	w.Header().Set("Content-Type", art.ContentType)
+	w.Header().Set("Content-Length", strconv.FormatInt(art.SizeBytes, 10))
+	w.Header().Set("X-Checksum-SHA256", art.SHA256)
+	_, _ = io.Copy(w, body)
+}
+
 // handleUploadArtifact streams a worker's partial result into blob storage. It
 // deliberately does not use the short request timeout — a large shard upload
 // would trip it — and reads identity from headers per the contract (§5.5).
@@ -220,7 +324,7 @@ func (s *Server) handleDownloadArtifact(w http.ResponseWriter, r *http.Request)
 		s.writeError(w, r, err)
 		return
 	}
-	defer body.Close()
+	defer func() { _ = body.Close() }()
 
 	w.Header().Set("Content-Type", art.ContentType)
 	w.Header().Set("Content-Length", strconv.FormatInt(art.SizeBytes, 10))
diff --git a/coordinator/internal/transport/http/server.go b/coordinator/internal/transport/http/server.go
index 6a65d60..109392c 100644
--- a/coordinator/internal/transport/http/server.go
+++ b/coordinator/internal/transport/http/server.go
@@ -18,6 +18,7 @@ import (
 type UseCases struct {
 	RegisterWorker   *usecase.RegisterWorker
 	CreateJob        *usecase.CreateJob
+	SubmitDataset    *usecase.SubmitDataset
 	ClaimTask        *usecase.ClaimTask
 	RenewLease       *usecase.RenewLease
 	CompleteTask     *usecase.CompleteTask
@@ -25,6 +26,7 @@ type UseCases struct {
 	GetJobStatus     *usecase.GetJobStatus
 	UploadArtifact   *usecase.UploadArtifact
 	DownloadArtifact *usecase.DownloadArtifact
+	GetTaskInput     *usecase.GetTaskInput
 }
 
 type Server struct {
@@ -54,8 +56,10 @@ func (s *Server) Handler(token string) http.Handler {
 	protected := http.NewServeMux()
 	protected.HandleFunc("POST /workers/register", s.handleRegister)
 	protected.HandleFunc("POST /jobs", s.handleCreateJob)
+	protected.HandleFunc("POST /jobs/upload", s.handleUploadDataset)
 	protected.HandleFunc("GET /jobs/{job_id}", s.handleGetJob)
 	protected.HandleFunc("POST /tasks/claim", s.handleClaim)
+	protected.HandleFunc("GET /tasks/{task_id}/input", s.handleGetTaskInput)
 	protected.HandleFunc("POST /tasks/{task_id}/heartbeat", s.handleHeartbeat)
 	protected.HandleFunc("POST /tasks/{task_id}/result", s.handleResult)
 	protected.HandleFunc("POST /tasks/{task_id}/failure", s.handleFailure)
diff --git a/coordinator/internal/usecase/dto.go b/coordinator/internal/usecase/dto.go
index d784b71..6491cbf 100644
--- a/coordinator/internal/usecase/dto.go
+++ b/coordinator/internal/usecase/dto.go
@@ -49,6 +49,21 @@ type CompleteTaskInput struct {
 	Metrics          map[string]any
 }
 
+type SubmitDatasetInput struct {
+	Workload     string
+	Parameters   map[string]any
+	RowsPerShard int
+	Filename     string
+	ContentType  string
+	Body         io.Reader
+}
+
+type SubmitDatasetResult struct {
+	JobID           uuid.UUID
+	TaskCount       int
+	InputArtifactID uuid.UUID
+}
+
 type UploadArtifactInput struct {
 	TaskID      uuid.UUID
 	WorkerID    string
diff --git a/coordinator/internal/usecase/upload.go b/coordinator/internal/usecase/upload.go
new file mode 100644
index 0000000..f04f582
--- /dev/null
+++ b/coordinator/internal/usecase/upload.go
@@ -0,0 +1,151 @@
+package usecase
+
+import (
+	"context"
+	"fmt"
+	"io"
+
+	"github.com/google/uuid"
+
+	"github.com/emil28092005/SciMesh/coordinator/internal/chunk"
+	"github.com/emil28092005/SciMesh/coordinator/internal/domain"
+)
+
+// SubmitDataset accepts an uploaded dataset, splits it into shard artifacts, and
+// creates the job with one task per shard — the coordinator-side counterpart of
+// a client submitting pre-chunked URIs.
+type SubmitDataset struct {
+	blobs     BlobStore
+	artifacts ArtifactRepository
+	jobs      JobRepository
+	tasks     TaskRepository
+	tx        TxManager
+	clk       Clock
+}
+
+func NewSubmitDataset(blobs BlobStore, artifacts ArtifactRepository, jobs JobRepository,
+	tasks TaskRepository, tx TxManager, clk Clock) *SubmitDataset {
+	return &SubmitDataset{blobs: blobs, artifacts: artifacts, jobs: jobs, tasks: tasks, tx: tx, clk: clk}
+}
+
+func (uc *SubmitDataset) Execute(ctx context.Context, in SubmitDatasetInput) (SubmitDatasetResult, error) {
+	now := uc.clk.Now()
+
+	job, err := domain.NewUploadedJob(in.Workload, in.Parameters, now)
+	if err != nil {
+		return SubmitDatasetResult{}, err
+	}
+
+	// Everything written to blob storage, so a failed transaction can undo it.
+	var putKeys []string
+	cleanup := func() {
+		for _, k := range putKeys {
+			_ = uc.blobs.Delete(ctx, k)
+		}
+	}
+
+	// 1. Stream the upload into the input artifact; we measure size and sha256.
+	input, err := domain.NewArtifact(job.ID, nil, domain.ArtifactInput, in.Filename, in.ContentType, now)
+	if err != nil {
+		return SubmitDatasetResult{}, err
+	}
+	sum, size, err := uc.blobs.Put(ctx, input.StorageKey, in.Body)
+	if err != nil {
+		return SubmitDatasetResult{}, err
+	}
+	putKeys = append(putKeys, input.StorageKey)
+	input.SetContent(sum, size)
+
+	// 2. Re-open the stored input and split it into shard artifacts + tasks.
+	shards := []*domain.Artifact{}
+	tasks := []*domain.Task{}
+	rc, err := uc.blobs.Open(ctx, input.StorageKey)
+	if err != nil {
+		cleanup()
+		return SubmitDatasetResult{}, err
+	}
+	splitErr := chunk.SplitTSV(rc, in.RowsPerShard, func(index int, shard io.Reader) error {
+		art, err := domain.NewArtifact(job.ID, nil, domain.ArtifactShard,
+			fmt.Sprintf("shard-%d.tsv", index), in.ContentType, now)
+		if err != nil {
+			return err
+		}
+		ssum, ssize, err := uc.blobs.Put(ctx, art.StorageKey, shard)
+		if err != nil {
+			return err
+		}
+		putKeys = append(putKeys, art.StorageKey)
+		art.SetContent(ssum, ssize)
+
+		task, err := domain.NewShardTask(job.ID, index, in.Workload, art.ID, ssum, in.Parameters, 0, now)
+		if err != nil {
+			return err
+		}
+		shards = append(shards, art)
+		tasks = append(tasks, task)
+		return nil
+	})
+	_ = rc.Close()
+	if splitErr != nil {
+		cleanup()
+		return SubmitDatasetResult{}, splitErr
+	}
+
+	// 3. Persist job + all artifacts + all tasks atomically.
+	err = uc.tx.WithinTx(ctx, func(ctx context.Context) error {
+		if err := uc.jobs.Insert(ctx, job); err != nil {
+			return err
+		}
+		if err := uc.artifacts.Insert(ctx, input); err != nil {
+			return err
+		}
+		for _, a := range shards {
+			if err := uc.artifacts.Insert(ctx, a); err != nil {
+				return err
+			}
+		}
+		return uc.tasks.InsertBatch(ctx, tasks)
+	})
+	if err != nil {
+		cleanup()
+		return SubmitDatasetResult{}, err
+	}
+
+	return SubmitDatasetResult{
+		JobID:           job.ID,
+		TaskCount:       len(tasks),
+		InputArtifactID: input.ID,
+	}, nil
+}
+
+// GetTaskInput resolves a task's input shard and opens it for streaming. The
+// caller closes the reader.
+type GetTaskInput struct {
+	tasks     TaskRepository
+	artifacts ArtifactRepository
+	blobs     BlobStore
+}
+
+func NewGetTaskInput(tasks TaskRepository, artifacts ArtifactRepository, blobs BlobStore) *GetTaskInput {
+	return &GetTaskInput{tasks: tasks, artifacts: artifacts, blobs: blobs}
+}
+
+func (uc *GetTaskInput) Execute(ctx context.Context, taskID uuid.UUID) (*domain.Artifact, io.ReadCloser, error) {
+	task, err := uc.tasks.Get(ctx, taskID)
+	if err != nil {
+		return nil, nil, err
+	}
+	if task.InputArtifactID == nil {
+		// A URI-based task keeps its input outside the coordinator.
+		return nil, nil, domain.ErrArtifactNotFound
+	}
+	art, err := uc.artifacts.Get(ctx, *task.InputArtifactID)
+	if err != nil {
+		return nil, nil, err
+	}
+	rc, err := uc.blobs.Open(ctx, art.StorageKey)
+	if err != nil {
+		return nil, nil, err
+	}
+	return art, rc, nil
+}
diff --git a/coordinator/migrations/0005_uploaded_input.down.sql b/coordinator/migrations/0005_uploaded_input.down.sql
new file mode 100644
index 0000000..87731e2
--- /dev/null
+++ b/coordinator/migrations/0005_uploaded_input.down.sql
@@ -0,0 +1,9 @@
+BEGIN;
+
+ALTER TABLE tasks DROP CONSTRAINT IF EXISTS ck_tasks_has_input;
+
+-- Restoring NOT NULL requires the columns to be populated; safe on a fresh DB.
+ALTER TABLE tasks ALTER COLUMN input_uri SET NOT NULL;
+ALTER TABLE jobs  ALTER COLUMN input_uri SET NOT NULL;
+
+COMMIT;
diff --git a/coordinator/migrations/0005_uploaded_input.up.sql b/coordinator/migrations/0005_uploaded_input.up.sql
new file mode 100644
index 0000000..04d79fb
--- /dev/null
+++ b/coordinator/migrations/0005_uploaded_input.up.sql
@@ -0,0 +1,13 @@
+BEGIN;
+
+-- Inputs can now arrive as uploaded artifacts (POST /jobs/upload), not only as
+-- external URIs. Relax the URI requirement and require every task to have an
+-- input one way or the other.
+ALTER TABLE jobs  ALTER COLUMN input_uri DROP NOT NULL;
+ALTER TABLE tasks ALTER COLUMN input_uri DROP NOT NULL;
+
+ALTER TABLE tasks ADD CONSTRAINT ck_tasks_has_input CHECK (
+    input_uri IS NOT NULL OR input_artifact_id IS NOT NULL
+);
+
+COMMIT;
diff --git a/coordinator/scripts/smoke.sh b/coordinator/scripts/smoke.sh
index 762b784..2d9a1f2 100755
--- a/coordinator/scripts/smoke.sh
+++ b/coordinator/scripts/smoke.sh
@@ -147,6 +147,56 @@ check "unknown json field → 400"           400 -X POST "${HOST}/tasks/claim" "
 	-d '{"worker_id":"w1","totally_unknown":1}'
 check "unknown job → 404"                  404 "${HOST}/jobs/00000000-0000-0000-0000-000000000000" "${auth[@]}"
 
+echo
+echo "dataset upload → chunking"
+# Upload a 5-row TSV split at 2 rows/shard → expect 3 shard tasks. The text
+# fields precede the file part, which the coordinator streams.
+up=$(curl -sS "${bearer[@]}" -X POST "${HOST}/jobs/upload" \
+	-F 'workload=similarity_search' \
+	-F 'parameters={"top_k":10}' \
+	-F 'chunk_rows=2' \
+	-F 'file=@-;filename=chembl.tsv;type=text/tab-separated-values' <<'TSV'
+id	smiles
+A	CC
+B	CCC
+C	CCCC
+D	CCCCC
+E	CCCCCC
+TSV
+)
+up_job=$(printf '%s' "$up" | python3 -c 'import json,sys;print(json.load(sys.stdin)["job_id"])' 2>/dev/null)
+up_count=$(printf '%s' "$up" | python3 -c 'import json,sys;print(json.load(sys.stdin)["task_count"])' 2>/dev/null)
+
+if [[ "$up_count" == "3" ]]; then
+	printf '  \033[32m✓\033[0m %-46s task_count=3\n' "POST /jobs/upload (5 rows / 2)"
+	pass=$((pass + 1))
+else
+	printf '  \033[31m✗\033[0m %-46s got task_count=%s, want 3\n' "POST /jobs/upload" "${up_count:-?}"
+	printf '      %s\n' "$up"
+	fail=$((fail + 1))
+fi
+
+# Claim one of this job's shard tasks and pull its input shard from the coordinator.
+up_input=""
+for _ in $(seq 1 30); do
+	c=$(curl -sS "${bearer[@]}" -H 'Content-Type: application/json' -X POST "${HOST}/tasks/claim" \
+		-d '{"worker_id":"up-w","capabilities":["similarity_search"]}')
+	[[ -z "$c" ]] && break
+	cj=$(printf '%s' "$c" | python3 -c 'import json,sys;print(json.load(sys.stdin)["job_id"])' 2>/dev/null)
+	[[ "$cj" != "$up_job" ]] && continue
+	up_input=$(printf '%s' "$c" | python3 -c 'import json,sys;print(json.load(sys.stdin)["input"]["uri"])' 2>/dev/null)
+	break
+done
+
+if [[ "$up_input" == /tasks/*/input ]]; then
+	printf '  \033[32m✓\033[0m %-46s %s\n' "claim → input.uri points at coordinator" "$up_input"
+	pass=$((pass + 1))
+else
+	printf '  \033[31m✗\033[0m %-46s got %q\n' "claim shard input.uri" "$up_input"
+	fail=$((fail + 1))
+fi
+check "download shard input"               200 "${HOST}${up_input}" "${bearer[@]}"
+
 echo
 curl -sS "${HOST}/jobs/${job_id}" "${auth[@]}"
 echo
diff --git a/docs/api-contract.md b/docs/api-contract.md
index e67346c..d025e7c 100644
--- a/docs/api-contract.md
+++ b/docs/api-contract.md
@@ -24,7 +24,8 @@ must be updated in the same change as any behaviour it describes.
 | `GET /jobs/{id}` | progress | ✅ done |
 | `PUT /tasks/{id}/artifacts/{name}` | upload partial | ✅ done |
 | `GET /artifacts/{id}/download` | download by id | ✅ done |
-| `GET /tasks/{id}/input` | download shard | ❌ needs input artifacts (upload+chunking) |
+| `POST /jobs/upload` | upload dataset, coordinator chunks it | ✅ done |
+| `GET /tasks/{id}/input` | download shard | ✅ done |
 
 ---
 
@@ -37,6 +38,28 @@ GET /health
 `200 {"status":"ok"}` when the database is reachable; `503 {"status":"unavailable"}`
 otherwise. Unauthenticated.
 
+## Submit a dataset (submitter-side)
+
+```http
+POST /jobs/upload
+Authorization: Bearer <token>
+Content-Type: multipart/form-data
+```
+
+Fields, in order (text fields first, file last — the file is streamed):
+`workload`, `parameters` (JSON), `chunk_rows` (int, default 1000), and the file
+part `file`. The coordinator stores the input, splits the TSV into shard
+artifacts (header repeated per shard), and creates one task per shard.
+
+`201`:
+
+```json
+{ "job_id": "uuid", "task_count": 3, "input_artifact_id": "uuid" }
+```
+
+Each resulting task's claim response carries `input.uri = /tasks/{id}/input`,
+served by §5.4.
+
 ## Register worker
 
 ```http