fix(landscape): guard redelivery, detach terminal writes, bound workers

F2: Execute had no status guard, so a redelivered or stale message reran a
finished run. Runs that are neither queued nor running are logged and acked
without work; "running" still executes so a worker that crashed mid-run
recovers.

F4: failRun, finishNodeFailed and MarkRunFailed wrote the terminal status on
the caller's context, which is exactly the context that is already cancelled
when the run failed because of a shutdown or a sibling node — the write was
refused and the run stayed stuck in "running". They now write on a
context.WithoutCancel copy with a 10s timeout; the consumer's best-effort
MarkRunFailed does the same.

F5: peak memory scaled with the host's core count. LP_MAX_WORKERS (default 8)
is now the total window-worker budget of a run and LP_MAX_NODES (default 2) the
node fan-out; each node gets max(1, workers/nodes) through the new
landscape.ComputeWithWorkers. Compute and service.ComputeFunc keep their
signatures: Compute delegates with MaxWorkersPerNode, and a legacy ComputeFunc
handed to NewLandscapeService is wrapped.

F6: the stage loop used a plain errgroup, so a failing node let its siblings
run to completion. It now uses errgroup.WithContext and passes the group
context into runNode, cancelling siblings mid-compute.

F7: wrap every float32 product in an explicit conversion so the compiler
cannot fuse it into an FMA, keeping the kernels bit-identical to numpy's
per-op rounding.

F8: README's builder package list now matches the Dockerfile (adds g++), and
the Landscape section documents the memory model and the two new knobs.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.env.example

@@ -10,3 +10,7 @@ S3_BUCKET: geofiles
 S3_USE_SSL: "false"
 
 DB_PORT=5423
+
+# Landscape Program parallelism (bounds worker peak memory)
+LP_MAX_WORKERS=8
+LP_MAX_NODES=2

README.md

@@ -232,6 +232,31 @@ one, an `sld_url` (`/dataset-groups/{id}/sld`). A node failure fails its stage;
 later stages are not started and the run ends `failed` with the message. Jobs are
 nacked without requeue, so there is no automatic retry — start a new run.
 
+### Memory and parallelism
+
+A run has two nested levels of parallelism: nodes of a stage run concurrently,
+and each node processes its windows with its own worker pool. Every worker holds
+one window buffer per input **and** per output, so the worker's peak resident set
+is roughly
+
+```
+nodes × workers-per-node × window_size² × (inputs + outputs) × 8 bytes
+```
+
+(the widest node, `20 c_conflicts`, has 6 inputs and 5 outputs). Two environment
+variables bound that product, independently of how many cores the host has:
+
+| Variable | Default | Meaning |
+| --- | --- | --- |
+| `LP_MAX_WORKERS` | `8` | Total window-worker budget shared by all nodes of a run. |
+| `LP_MAX_NODES` | `2` | How many graph nodes of one stage run at the same time. |
+
+Each node gets `max(1, LP_MAX_WORKERS / LP_MAX_NODES)` workers, further capped by
+`GOMAXPROCS` and by the number of windows, so the total stays at
+`LP_MAX_WORKERS`. At the defaults and `window_size: 2048` that is about
+8 × 2048² × 11 × 8 B ≈ 2.9 GiB worst case — lower `LP_MAX_WORKERS` (or
+`window_size`) on a small host, raise it on a large one.
+
 ### Build requirements
 
 The raster math uses [godal](https://github.com/airbusgeo/godal), a **cgo**
@@ -244,7 +269,7 @@ go build ./...             # cgo is on by default for a native build
 ```
 
 `build/package/Dockerfile` already handles the image: the builder stage adds
-`gdal-dev gcc musl-dev pkgconfig` and builds with `CGO_ENABLED=1`, and the
+`gdal-dev gcc g++ musl-dev pkgconfig` and builds with `CGO_ENABLED=1`, and the
 runtime stage installs `gdal` (the shared library godal needs) plus `gdal-tools`
 (`gdal_translate`/`gdalinfo` for the COG conversion).
 

configs/.env.example

@@ -28,3 +28,7 @@ RABBITMQ_QUEUE=gis.events.example
 
 # Host port mapping for the postgres container (docker-compose)
 DB_PORT=5432
+
+# Landscape Program parallelism (bounds worker peak memory)
+LP_MAX_WORKERS=8
+LP_MAX_NODES=2

internal/app/app.go

@@ -12,7 +12,6 @@ import (
 	"gis/api"
 	"gis/internal/config"
 	"gis/internal/domain"
-	"gis/internal/landscape"
 	"gis/internal/messaging/rabbitmq"
 	"gis/internal/parser"
 	"gis/internal/platform/logger"
@@ -92,9 +91,15 @@ func New(ctx context.Context) (*App, error) {
 		categories: service.NewCategoryService(categoryRepo),
 		datasets:   datasetsSvc,
 		groups:     service.NewDatasetGroupService(groupRepo, datasetRepo, store),
+		// A nil ComputeFunc selects landscape.ComputeWithWorkers, so each node
+		// gets the per-node share of the configured worker budget.
 		landscape: service.NewLandscapeService(
 			lpRepo, datasetRepo, groupRepo, categoryRepo, datasetsSvc, store,
-			lpJobs, raster.NewGodalIO(), landscape.Compute, log,
+			lpJobs, raster.NewGodalIO(), nil, log,
+			service.LandscapeOptions{
+				MaxWorkers:         cfg.Landscape.MaxWorkers,
+				MaxConcurrentNodes: cfg.Landscape.MaxConcurrentNodes,
+			},
 		),
 		eventRepo: eventRepo,
 	}, nil

internal/config/config.go

@@ -16,6 +16,7 @@ type Config struct {
 	DB        DBConfig
 	S3        S3Config
 	RabbitMQ  RabbitMQConfig
+	Landscape LandscapeConfig
 }
 
 // HTTPConfig configures the HTTP server.
@@ -58,6 +59,19 @@ type RabbitMQConfig struct {
 	Queue    string `env:"RABBITMQ_QUEUE" envDefault:"gis.events.example"`
 }
 
+// LandscapeConfig bounds the Landscape Program's parallelism, and with it the
+// worker's peak memory: a run holds up to MaxConcurrentNodes nodes in flight,
+// each running a pool of MaxWorkers/MaxConcurrentNodes goroutines that own one
+// window buffer per input and output. The defaults (8 total workers spread
+// over 2 nodes) keep that product bounded regardless of how many cores the
+// host has.
+type LandscapeConfig struct {
+	// MaxWorkers is the total window-worker budget shared by all nodes of a run.
+	MaxWorkers int `env:"LP_MAX_WORKERS" envDefault:"8"`
+	// MaxConcurrentNodes is how many graph nodes of one stage run at a time.
+	MaxConcurrentNodes int `env:"LP_MAX_NODES" envDefault:"2"`
+}
+
 // Load reads configuration from the environment, loading an optional .env file
 // from the current working directory first.
 func Load() (*Config, error) {

internal/landscape/compute.go

@@ -13,13 +13,27 @@ import (
 	"golang.org/x/sync/errgroup"
 )
 
-// Compute runs one node over its input rasters. See the package doc for the
+// MaxWorkersPerNode is the per-node worker cap Compute uses. Peak memory is
-// concurrency model: windows are processed by a worker pool; each worker owns
+// roughly nodes x workers x window^2 x (inputs+outputs), so callers that run
+// several nodes at once should divide their total worker budget between them
+// and call ComputeWithWorkers instead.
+const MaxWorkersPerNode = 8
+
+// Compute runs one node over its input rasters with the default per-node
+// worker cap (MaxWorkersPerNode). See ComputeWithWorkers.
+func Compute(ctx context.Context, rio raster.IO, node Node, inputs map[string]string, outDir string, p Params) (map[string]string, error) {
+	return ComputeWithWorkers(ctx, rio, node, inputs, outDir, p, MaxWorkersPerNode)
+}
+
+// ComputeWithWorkers runs one node over its input rasters with an explicit
+// worker cap. See the package doc for the concurrency model: windows are
+// processed by a worker pool of at most workers goroutines; each worker owns
 // its own Reader handles (GDAL datasets are not goroutine-safe) and writes are
 // serialised per output. Window order does not affect the result. On any
-// error, no output files are left behind: Compute best-effort removes every
+// error, no output files are left behind: ComputeWithWorkers best-effort
-// output it created before returning.
+// removes every output it created before returning. A workers value below 1 is
-func Compute(ctx context.Context, rio raster.IO, node Node, inputs map[string]string, outDir string, p Params) (map[string]string, error) {
+// treated as 1.
+func ComputeWithWorkers(ctx context.Context, rio raster.IO, node Node, inputs map[string]string, outDir string, p Params, workers int) (map[string]string, error) {
 	p = p.WithDefaults()
 	if p.WindowSize <= 0 {
 		// WithDefaults only fills in a zero value; guard against a negative
@@ -75,8 +89,8 @@ func Compute(ctx context.Context, rio raster.IO, node Node, inputs map[string]st
 	// per-window input/output buffers, and nodes can have many inputs and
 	// outputs (e.g. node 20: 6 inputs, 5 outputs), so an unbounded worker
 	// count multiplies memory with core count and with concurrently running
-	// nodes.
+	// nodes. The caller's budget is the third bound.
-	workers := min(runtime.GOMAXPROCS(0), len(windows), 8)
+	workers = min(runtime.GOMAXPROCS(0), len(windows), max(1, workers))
 	for w := 0; w < workers; w++ {
 		eg.Go(func() error {
 			readers, err := openAll(gctx, rio, node, paths)

internal/landscape/compute_test.go

@@ -217,3 +217,36 @@ func TestRemoveOutputs_DeletesFiles(t *testing.T) {
 		}
 	}
 }
+
+// TestComputeWithWorkers_RespectsCap checks the caller's worker budget bounds
+// the pool: each pool worker opens one reader per input and holds a buffer per
+// input and output, so the open count bounds peak memory. checkGrids opens one
+// extra set of handles before the pool starts, hence the (workers+1) bound.
+func TestComputeWithWorkers_RespectsCap(t *testing.T) {
+	node, _ := NodeByCode("10")
+	inputs := len(node.Inputs)
+
+	for _, workers := range []int{1, 2, 4, 0, -3} {
+		t.Run(fmt.Sprintf("workers=%d", workers), func(t *testing.T) {
+			fio := newFakeIO()
+			g := grid(64, 64)
+			fio.put("z.tif", g, constRaster(64, 64, 2))
+			fio.put("u.tif", g, constRaster(64, 64, 4))
+			p := DefaultParams()
+			p.WindowSize = 8 // 64 windows, so the pool is never window-bound
+
+			if _, err := ComputeWithWorkers(context.Background(), fio, node,
+				map[string]string{OutZIntegrated: "z.tif", OutUIntegrated: "u.tif"}, "/out", p, workers); err != nil {
+				t.Fatal(err)
+			}
+
+			effective := max(1, workers)
+			if got, limit := fio.openCount(), (effective+1)*inputs; got > limit {
+				t.Fatalf("opened %d readers with workers=%d, want at most %d", got, workers, limit)
+			}
+			if fio.openCount() < inputs {
+				t.Fatalf("opened %d readers, want at least one set of %d", fio.openCount(), inputs)
+			}
+		})
+	}
+}

internal/landscape/fakeio_test.go

@@ -19,6 +19,17 @@ type fakeIO struct {
 	// mid-run I/O failure.
 	failReadAfter map[string]int
 	readCounts    map[string]int
+
+	// opens counts every successful Open. Each pool worker opens one reader
+	// per input, so the count bounds the number of concurrent handles.
+	opens int
+}
+
+// openCount returns how many readers have been opened so far.
+func (f *fakeIO) openCount() int {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.opens
 }
 
 type fakeRaster struct {
@@ -96,6 +107,7 @@ func (f *fakeIO) Open(_ context.Context, path string) (raster.Reader, error) {
 	if !ok {
 		return nil, fmt.Errorf("fake: %s not found", path)
 	}
+	f.opens++
 	return &fakeReader{f: f, path: path, r: r}, nil
 }
 

internal/landscape/kernels.go

@@ -34,7 +34,9 @@ func kernelZIntegrated(in [][]float64, out [][]int16, _ Params) {
 			out[0][i] = NoData
 			continue
 		}
-		score := float32(0.25)*float32(z1) + float32(0.25)*float32(z2) + float32(0.25)*float32(z3) + float32(0.25)*float32(z4)
+		// explicit conversions forbid FMA fusion so results match numpy's per-op rounding
+		score := float32(float32(0.25)*float32(z1)) + float32(float32(0.25)*float32(z2)) +
+			float32(float32(0.25)*float32(z3)) + float32(float32(0.25)*float32(z4))
 		out[0][i] = classify(score)
 	}
 }
@@ -49,14 +51,15 @@ func kernelUIntegrated(in [][]float64, out [][]int16, _ Params) {
 			out[0][i] = NoData
 			continue
 		}
-		num := float32(0.25)*float32(water) + float32(0.25)*float32(soil)
+		// explicit conversions forbid FMA fusion so results match numpy's per-op rounding
+		num := float32(float32(0.25)*float32(water)) + float32(float32(0.25)*float32(soil))
 		den := float32(0.5)
 		if cropOK {
-			num += float32(0.25) * float32(crop)
+			num += float32(float32(0.25) * float32(crop))
 			den += 0.25
 		}
 		if vegOK {
-			num += float32(0.25) * float32(veg)
+			num += float32(float32(0.25) * float32(veg))
 			den += 0.25
 		}
 		out[0][i] = classify(num / den)

internal/messaging/rabbitmq/landscape_consumer.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"log/slog"
+	"time"
 
 	"github.com/google/uuid"
 	amqp "github.com/rabbitmq/amqp091-go"
@@ -15,6 +16,9 @@ const (
 	LandscapeRunRoutingKey = "landscape.run"
 	// LandscapeRunQueue receives Landscape Program run jobs.
 	LandscapeRunQueue = "gis.landscape.run"
+	// markRunFailedTimeout bounds the best-effort terminal status write made
+	// after Execute failed, on a context detached from the delivery's.
+	markRunFailedTimeout = 10 * time.Second
 )
 
 // LandscapeJob is the message body for a Landscape Program run job.
@@ -72,9 +76,14 @@ func (h landscapeHandler) Handle(ctx context.Context, d amqp.Delivery) error {
 		// status write), since Execute already marks the run failed for every
 		// node failure. Best-effort: log if marking fails, but still return the
 		// original error so the delivery is nacked.
-		if markErr := h.proc.MarkRunFailed(ctx, job.RunID, err.Error()); markErr != nil {
+		// Detached from ctx: Execute may well have failed *because* ctx was
+		// cancelled (shutdown), and the write must still land or the run stays
+		// "running" forever.
+		mctx, cancel := context.WithTimeout(context.WithoutCancel(ctx), markRunFailedTimeout)
+		if markErr := h.proc.MarkRunFailed(mctx, job.RunID, err.Error()); markErr != nil {
 			h.log.Error("mark landscape run failed", "run_id", job.RunID, "error", markErr)
 		}
+		cancel()
 	}
 	return err
 }

internal/service/landscape.go

@@ -11,7 +11,6 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
-	"runtime"
 	"sort"
 	"sync"
 	"time"
@@ -29,6 +28,47 @@ import (
 // mirrors landscape.Compute so tests can substitute a stub.
 type ComputeFunc func(ctx context.Context, rio raster.IO, node landscape.Node, inputs map[string]string, outDir string, p landscape.Params) (map[string]string, error)
 
+// ComputeWithWorkersFunc is ComputeFunc plus an explicit per-node worker cap.
+// It mirrors landscape.ComputeWithWorkers.
+type ComputeWithWorkersFunc func(ctx context.Context, rio raster.IO, node landscape.Node, inputs map[string]string, outDir string, p landscape.Params, workers int) (map[string]string, error)
+
+// Default bounds on a run's parallelism, mirroring config.LandscapeConfig.
+const (
+	// DefaultMaxWorkers is the total window-worker budget of one run.
+	DefaultMaxWorkers = 8
+	// DefaultMaxConcurrentNodes is how many nodes of a stage run at a time.
+	DefaultMaxConcurrentNodes = 2
+)
+
+// terminalWriteTimeout bounds a terminal status write made on a context that
+// has already been cancelled (see terminalCtx).
+const terminalWriteTimeout = 10 * time.Second
+
+// LandscapeOptions bounds a run's parallelism, and with it the worker's peak
+// memory: MaxConcurrentNodes nodes run at a time, and they share the
+// MaxWorkers window-worker budget. Zero or negative values fall back to the
+// defaults.
+type LandscapeOptions struct {
+	MaxWorkers         int
+	MaxConcurrentNodes int
+}
+
+func (o LandscapeOptions) withDefaults() LandscapeOptions {
+	if o.MaxWorkers < 1 {
+		o.MaxWorkers = DefaultMaxWorkers
+	}
+	if o.MaxConcurrentNodes < 1 {
+		o.MaxConcurrentNodes = DefaultMaxConcurrentNodes
+	}
+	return o
+}
+
+// workersPerNode splits the total worker budget over the concurrently running
+// nodes, so nodes x workers stays at MaxWorkers. Always at least 1.
+func (o LandscapeOptions) workersPerNode() int {
+	return max(1, o.MaxWorkers/o.MaxConcurrentNodes)
+}
+
 // LandscapeRepository is the persistence behaviour LandscapeService needs.
 type LandscapeRepository interface {
 	CreateRun(ctx context.Context, run domain.LPRun) (domain.LPRun, error)
@@ -115,7 +155,12 @@ type LandscapeService struct {
 	store      ObjectStore
 	jobs       LandscapeJobEnqueuer
 	rio        raster.IO
+	// compute is the legacy worker-count-agnostic entry point, kept so an
+	// existing ComputeFunc still wires up; runNode always calls
+	// computeWithWorkers, which wraps compute when one was provided.
 	compute            ComputeFunc
+	computeWithWorkers ComputeWithWorkersFunc
+	opts               LandscapeOptions
 	log                *slog.Logger
 }
 
@@ -123,7 +168,11 @@ type LandscapeService struct {
 // repositories (input resolution), the category reader (the "landscape"
 // category every result is filed under), the dataset publisher (result
 // datasets and slot uploads), the object store (input downloads), the job
-// enqueuer, and the raster IO / compute function the graph runs on.
+// enqueuer, and the raster IO / compute function the graph runs on. Pass a nil
+// compute (the production wiring) to run landscape.ComputeWithWorkers with the
+// per-node share of opts.MaxWorkers; a non-nil ComputeFunc is honoured for
+// backward compatibility but never sees the worker cap. opts bounds the run's
+// parallelism; zero fields fall back to the package defaults.
 func NewLandscapeService(
 	runs LandscapeRepository,
 	datasets DatasetRepository,
@@ -135,7 +184,16 @@ func NewLandscapeService(
 	rio raster.IO,
 	compute ComputeFunc,
 	log *slog.Logger,
+	opts LandscapeOptions,
 ) *LandscapeService {
+	// Default to the workers-aware entry point; wrap a supplied legacy
+	// ComputeFunc (which has no worker parameter) when one is given.
+	withWorkers := ComputeWithWorkersFunc(landscape.ComputeWithWorkers)
+	if compute != nil {
+		withWorkers = func(ctx context.Context, rio raster.IO, node landscape.Node, inputs map[string]string, outDir string, p landscape.Params, _ int) (map[string]string, error) {
+			return compute(ctx, rio, node, inputs, outDir, p)
+		}
+	}
 	return &LandscapeService{
 		runs:               runs,
 		datasets:           datasets,
@@ -146,6 +204,8 @@ func NewLandscapeService(
 		jobs:               jobs,
 		rio:                rio,
 		compute:            compute,
+		computeWithWorkers: withWorkers,
+		opts:               opts.withDefaults(),
 		log:                log,
 	}
 }
@@ -344,7 +404,9 @@ func (s *LandscapeService) Results(ctx context.Context) ([]ResultInfo, error) {
 // MarkRunFailed records a terminal failure on a run so it does not stay stuck
 // in an in-progress status.
 func (s *LandscapeService) MarkRunFailed(ctx context.Context, runID uuid.UUID, reason string) error {
-	return s.runs.SetRunStatus(ctx, runID, domain.LPRunFailed, &reason)
+	wctx, cancel := terminalCtx(ctx)
+	defer cancel()
+	return s.runs.SetRunStatus(wctx, runID, domain.LPRunFailed, &reason)
 }
 
 // Execute runs the whole graph for one run: stages in order, nodes within a
@@ -355,6 +417,13 @@ func (s *LandscapeService) Execute(ctx context.Context, runID uuid.UUID) error {
 	if err != nil {
 		return err
 	}
+	// A redelivered or stale message must not rerun a finished run. "running"
+	// is allowed through so a run whose worker crashed mid-flight still
+	// recovers on redelivery.
+	if run.Status != domain.LPRunQueued && run.Status != domain.LPRunRunning {
+		s.log.Info("landscape run already terminal, ignoring redelivery", "run_id", runID, "status", run.Status)
+		return nil
+	}
 
 	var params landscape.Params
 	if len(run.Params) > 0 {
@@ -382,15 +451,18 @@ func (s *LandscapeService) Execute(ctx context.Context, runID uuid.UUID) error {
 
 	state := &runState{produced: map[string]uuid.UUID{}}
 	for _, stage := range landscape.Stages() {
-		var g errgroup.Group
+		// WithContext so the first failing node cancels its siblings: Compute
-		// Each node's Compute spins its own worker pool (up to
+		// honours cancellation, so a doomed stage stops reading rasters
-		// min(GOMAXPROCS, windows, 8) workers, each holding a window buffer per
+		// instead of running to completion. Terminal status writes use
-		// input band), so peak memory is the product of the two limits. Bound
+		// terminalCtx, so they still land on the cancelled context.
-		// the node fan-out here so that product stays sane: without a limit all
+		g, gctx := errgroup.WithContext(ctx)
-		// four stage-0 nodes would run at once and multiply Compute's own cap.
+		// Each node's Compute spins its own worker pool (each worker holding a
-		g.SetLimit(maxConcurrentNodes())
+		// window buffer per input band), so peak memory is the product of the
+		// two limits. Bound the node fan-out here and split the worker budget
+		// over it so that product stays at opts.MaxWorkers.
+		g.SetLimit(s.opts.MaxConcurrentNodes)
 		for _, node := range stage {
-			g.Go(func() error { return s.runNode(ctx, run, node, params, cat, state) })
+			g.Go(func() error { return s.runNode(gctx, run, node, params, cat, state) })
 		}
 		// Wait for every node of the stage: each one records its own outcome,
 		// and a sibling's failure must not leave a node half-recorded.
@@ -402,10 +474,20 @@ func (s *LandscapeService) Execute(ctx context.Context, runID uuid.UUID) error {
 	return s.runs.SetRunStatus(ctx, runID, domain.LPRunSucceeded, nil)
 }
 
+// terminalCtx derives a bounded context that outlives the cancellation of ctx.
+// Terminal status writes must happen even when the run failed *because* the
+// context was cancelled (shutdown, a sibling node failing the stage); on the
+// original context they would be refused and leave the run stuck in "running".
+func terminalCtx(ctx context.Context) (context.Context, context.CancelFunc) {
+	return context.WithTimeout(context.WithoutCancel(ctx), terminalWriteTimeout)
+}
+
 // failRun marks the run failed with cause's message and returns cause.
 func (s *LandscapeService) failRun(ctx context.Context, runID uuid.UUID, cause error) error {
 	msg := cause.Error()
-	if err := s.runs.SetRunStatus(ctx, runID, domain.LPRunFailed, &msg); err != nil {
+	wctx, cancel := terminalCtx(ctx)
+	defer cancel()
+	if err := s.runs.SetRunStatus(wctx, runID, domain.LPRunFailed, &msg); err != nil {
 		s.log.Error("mark landscape run failed", "run_id", runID, "error", err)
 	}
 	return cause
@@ -473,7 +555,9 @@ func (s *LandscapeService) runNode(ctx context.Context, run domain.LPRun, node l
 // finishNodeFailed records the failure on the node and returns the cause.
 func (s *LandscapeService) finishNodeFailed(ctx context.Context, runID uuid.UUID, node landscape.Node, cause error) error {
 	msg := cause.Error()
-	if err := s.runs.SetNodeFinished(ctx, runID, node.Code, domain.LPNodeFailed, nil, &msg); err != nil {
+	wctx, cancel := terminalCtx(ctx)
+	defer cancel()
+	if err := s.runs.SetNodeFinished(wctx, runID, node.Code, domain.LPNodeFailed, nil, &msg); err != nil {
 		s.log.Error("mark landscape node failed", "run_id", runID, "node", node.Code, "error", err)
 	}
 	return cause
@@ -583,7 +667,7 @@ func (s *LandscapeService) computeNode(
 		paths[group] = path
 	}
 
-	outPaths, err := s.compute(ctx, s.rio, node, paths, dir, params)
+	outPaths, err := s.computeWithWorkers(ctx, s.rio, node, paths, dir, params, s.opts.workersPerNode())
 	if err != nil {
 		return nil, err
 	}
@@ -693,21 +777,6 @@ func knownGroup(code string) bool {
 	return ok
 }
 
-// maxConcurrentNodes caps how many graph nodes of one stage run at the same
-// time. Compute already parallelises within a node, so half the CPUs (at most
-// 4, the widest stage) is enough to keep the machine busy without letting the
-// two levels of parallelism multiply into an out-of-memory.
-func maxConcurrentNodes() int {
-	n := runtime.GOMAXPROCS(0) / 2
-	if n < 1 {
-		n = 1
-	}
-	if n > 4 {
-		n = 4
-	}
-	return n
-}
-
 // maxStage returns the highest stage number in the graph.
 func maxStage() int {
 	highest := 0

internal/service/landscape_test.go

@@ -65,12 +65,63 @@ func (r *lockedDatasetRepo) LatestInGroup(ctx context.Context, groupID uuid.UUID
 }
 
 // stubLPRepo is an in-memory LandscapeRepository for tests.
+// lpStatusWrite records one SetRunStatus call and whether the context it was
+// handed was still live.
+type lpStatusWrite struct {
+	status domain.LPRunStatus
+	ctxErr error
+}
+
+// lpNodeWrite records one SetNodeFinished call the same way.
+type lpNodeWrite struct {
+	code   string
+	status domain.LPNodeStatus
+	ctxErr error
+}
+
 type stubLPRepo struct {
 	mu           sync.Mutex
 	runs         map[uuid.UUID]*domain.LPRun
 	order        []uuid.UUID
 	reuseLookups []string
 	clock        int64
+	statusWrites []lpStatusWrite
+	nodeWrites   []lpNodeWrite
+}
+
+// statusesWritten returns the run statuses written so far, in order.
+func (r *stubLPRepo) statusesWritten() []domain.LPRunStatus {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	out := make([]domain.LPRunStatus, 0, len(r.statusWrites))
+	for _, w := range r.statusWrites {
+		out = append(out, w.status)
+	}
+	return out
+}
+
+// statusWrite returns the last write recording the given status.
+func (r *stubLPRepo) statusWrite(status domain.LPRunStatus) (lpStatusWrite, bool) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	for i := len(r.statusWrites) - 1; i >= 0; i-- {
+		if r.statusWrites[i].status == status {
+			return r.statusWrites[i], true
+		}
+	}
+	return lpStatusWrite{}, false
+}
+
+// nodeWrite returns the last SetNodeFinished write recording the given status.
+func (r *stubLPRepo) nodeWrite(status domain.LPNodeStatus) (lpNodeWrite, bool) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	for i := len(r.nodeWrites) - 1; i >= 0; i-- {
+		if r.nodeWrites[i].status == status {
+			return r.nodeWrites[i], true
+		}
+	}
+	return lpNodeWrite{}, false
 }
 
 func newStubLPRepo() *stubLPRepo {
@@ -170,9 +221,10 @@ func (r *stubLPRepo) CountRuns(_ context.Context) (int, error) {
 	return len(r.runs), nil
 }
 
-func (r *stubLPRepo) SetRunStatus(_ context.Context, id uuid.UUID, status domain.LPRunStatus, errMsg *string) error {
+func (r *stubLPRepo) SetRunStatus(ctx context.Context, id uuid.UUID, status domain.LPRunStatus, errMsg *string) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
+	r.statusWrites = append(r.statusWrites, lpStatusWrite{status: status, ctxErr: ctx.Err()})
 	run, ok := r.runs[id]
 	if !ok {
 		return domain.ErrNotFound
@@ -219,9 +271,10 @@ func (r *stubLPRepo) SetNodeStarted(_ context.Context, runID uuid.UUID, code, fi
 	return nil
 }
 
-func (r *stubLPRepo) SetNodeFinished(_ context.Context, runID uuid.UUID, code string, status domain.LPNodeStatus, outputs []domain.LPDatasetRef, errMsg *string) error {
+func (r *stubLPRepo) SetNodeFinished(ctx context.Context, runID uuid.UUID, code string, status domain.LPNodeStatus, outputs []domain.LPDatasetRef, errMsg *string) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
+	r.nodeWrites = append(r.nodeWrites, lpNodeWrite{code: code, status: status, ctxErr: ctx.Err()})
 	n, err := r.node(runID, code)
 	if err != nil {
 		return err
@@ -355,6 +408,9 @@ func (j *stubLPJobs) EnqueueRun(_ context.Context, runID uuid.UUID) error {
 // stubComputeCall records one invocation of the compute stub.
 type stubComputeCall struct {
 	node string
+	// workers is the per-node worker cap the service passed, or -1 when the
+	// call came through the legacy worker-agnostic ComputeFunc.
+	workers int
 	inputs  map[string]string
 	// bodies holds each input file's content at call time; seedDataset stores
 	// each object under its own storage key as its body, so a test can tell
@@ -369,11 +425,47 @@ type stubCompute struct {
 	mu    sync.Mutex
 	calls []stubComputeCall
 	errs  map[string]error
+	// waitForCancel names nodes whose compute blocks until its context is
+	// cancelled (or the deadline below elapses), so a test can observe whether
+	// a sibling's failure cancelled them.
+	waitForCancel map[string]bool
+	sawCancel     map[string]bool
 }
 
-func newStubCompute() *stubCompute { return &stubCompute{errs: map[string]error{}} }
+func newStubCompute() *stubCompute {
+	return &stubCompute{errs: map[string]error{}, waitForCancel: map[string]bool{}, sawCancel: map[string]bool{}}
+}
+
+// fn is a legacy service.ComputeFunc: it sees no worker cap.
+func (c *stubCompute) fn(ctx context.Context, rio raster.IO, node landscape.Node, inputs map[string]string, outDir string, p landscape.Params) (map[string]string, error) {
+	return c.fnWithWorkers(ctx, rio, node, inputs, outDir, p, -1)
+}
+
+// observedCancel reports whether the node's compute saw a cancelled context.
+func (c *stubCompute) observedCancel(code string) bool {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.sawCancel[code]
+}
+
+func (c *stubCompute) fnWithWorkers(ctx context.Context, _ raster.IO, node landscape.Node, inputs map[string]string, outDir string, p landscape.Params, workers int) (map[string]string, error) {
+	c.mu.Lock()
+	wait := c.waitForCancel[node.Code]
+	c.mu.Unlock()
+	if wait {
+		select {
+		case <-ctx.Done():
+		case <-time.After(5 * time.Second):
+		}
+		c.mu.Lock()
+		c.sawCancel[node.Code] = ctx.Err() != nil
+		c.mu.Unlock()
+	}
+	// The real Compute honours cancellation, so the stub must too.
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
 
-func (c *stubCompute) fn(_ context.Context, _ raster.IO, node landscape.Node, inputs map[string]string, outDir string, p landscape.Params) (map[string]string, error) {
 	in := map[string]string{}
 	bodies := map[string]string{}
 	for k, v := range inputs {
@@ -386,7 +478,7 @@ func (c *stubCompute) fn(_ context.Context, _ raster.IO, node landscape.Node, in
 	}
 
 	c.mu.Lock()
-	c.calls = append(c.calls, stubComputeCall{node: node.Code, inputs: in, bodies: bodies, params: p})
+	c.calls = append(c.calls, stubComputeCall{node: node.Code, workers: workers, inputs: in, bodies: bodies, params: p})
 	err := c.errs[node.Code]
 	c.mu.Unlock()
 	if err != nil {
@@ -453,6 +545,12 @@ type lpFixture struct {
 }
 
 func newLPFixture(t *testing.T) *lpFixture {
+	t.Helper()
+	return newLPFixtureWith(t, LandscapeOptions{})
+}
+
+// newLPFixtureWith builds the fixture with explicit parallelism options.
+func newLPFixtureWith(t *testing.T, opts LandscapeOptions) *lpFixture {
 	t.Helper()
 	ctx := context.Background()
 
@@ -482,7 +580,11 @@ func newLPFixture(t *testing.T) *lpFixture {
 	comp := newStubCompute()
 	log := slog.New(slog.NewTextHandler(io.Discard, nil))
 
-	svc := NewLandscapeService(runs, datasets, groups, cats, pub, store, jobs, nil, comp.fn, log)
+	svc := NewLandscapeService(runs, datasets, groups, cats, pub, store, jobs, nil, nil, log, opts)
+	// Substitute the workers-aware stub so tests can see the per-node cap the
+	// service computes; NewLandscapeService's legacy-ComputeFunc wrapping is
+	// covered separately.
+	svc.computeWithWorkers = comp.fnWithWorkers
 	return &lpFixture{
 		svc: svc, runs: runs, datasets: datasets, groups: groups, cats: cats,
 		pub: pub, store: store, jobs: jobs, compute: comp, category: cat,
@@ -1216,3 +1318,203 @@ func TestLandscapeService_Execute_OverridePinsInputOverFresherDataset(t *testing
 		t.Fatalf("node 01 input for %s = %v, want the freshest %v", landscape.SlotUVeg, got, newest.ID)
 	}
 }
+
+// F2: a redelivered message for a finished run must be acked without rerunning.
+func TestLandscapeService_Execute_IgnoresTerminalRun(t *testing.T) {
+	f := newLPFixture(t)
+	ctx := context.Background()
+	f.seedAllSlots(t)
+
+	run, err := f.svc.CreateRun(ctx, RunInput{})
+	if err != nil {
+		t.Fatalf("CreateRun: %v", err)
+	}
+	if err := f.runs.SetRunStatus(ctx, run.ID, domain.LPRunSucceeded, nil); err != nil {
+		t.Fatal(err)
+	}
+	f.runs.mu.Lock()
+	f.runs.statusWrites = nil
+	f.runs.mu.Unlock()
+
+	if err := f.svc.Execute(ctx, run.ID); err != nil {
+		t.Fatalf("Execute on a terminal run must ack, got %v", err)
+	}
+	if n := f.compute.count(); n != 0 {
+		t.Fatalf("compute called %d times for a terminal run", n)
+	}
+	if got := f.runs.statusesWritten(); len(got) != 0 {
+		t.Fatalf("no status write expected, got %v", got)
+	}
+	got, err := f.svc.GetRun(ctx, run.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Status != domain.LPRunSucceeded {
+		t.Fatalf("run status changed to %s", got.Status)
+	}
+}
+
+// F2: a "running" run is still executed, so a worker that crashed mid-run
+// recovers on redelivery.
+func TestLandscapeService_Execute_RerunsRunningRun(t *testing.T) {
+	f := newLPFixture(t)
+	ctx := context.Background()
+	f.seedAllSlots(t)
+
+	run, err := f.svc.CreateRun(ctx, RunInput{})
+	if err != nil {
+		t.Fatalf("CreateRun: %v", err)
+	}
+	if err := f.runs.SetRunStatus(ctx, run.ID, domain.LPRunRunning, nil); err != nil {
+		t.Fatal(err)
+	}
+	if err := f.svc.Execute(ctx, run.ID); err != nil {
+		t.Fatalf("Execute: %v", err)
+	}
+	if f.compute.count() == 0 {
+		t.Fatal("a running run must be executed on redelivery")
+	}
+}
+
+// F4: terminal status writes must land even when the caller's context is dead.
+func TestLandscapeService_Execute_TerminalWritesSurviveCancelledContext(t *testing.T) {
+	f := newLPFixture(t)
+	f.seedAllSlots(t)
+
+	run, err := f.svc.CreateRun(context.Background(), RunInput{})
+	if err != nil {
+		t.Fatalf("CreateRun: %v", err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	if err := f.svc.Execute(ctx, run.ID); err == nil {
+		t.Fatal("expected Execute to fail on a cancelled context")
+	}
+
+	got, err := f.svc.GetRun(context.Background(), run.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Status != domain.LPRunFailed {
+		t.Fatalf("run status = %s, want failed", got.Status)
+	}
+	w, ok := f.runs.statusWrite(domain.LPRunFailed)
+	if !ok {
+		t.Fatal("no failed status write recorded")
+	}
+	if w.ctxErr != nil {
+		t.Fatalf("terminal run status write got a cancelled context: %v", w.ctxErr)
+	}
+	nw, ok := f.runs.nodeWrite(domain.LPNodeFailed)
+	if !ok {
+		t.Fatal("no failed node write recorded")
+	}
+	if nw.ctxErr != nil {
+		t.Fatalf("terminal node write got a cancelled context: %v", nw.ctxErr)
+	}
+}
+
+// F4: MarkRunFailed is the consumer's last resort and must not need a live ctx.
+func TestLandscapeService_MarkRunFailed_IgnoresCancelledContext(t *testing.T) {
+	f := newLPFixture(t)
+	run, err := f.svc.CreateRun(context.Background(), RunInput{})
+	if err != nil {
+		t.Fatalf("CreateRun: %v", err)
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	if err := f.svc.MarkRunFailed(ctx, run.ID, "boom"); err != nil {
+		t.Fatalf("MarkRunFailed: %v", err)
+	}
+	w, ok := f.runs.statusWrite(domain.LPRunFailed)
+	if !ok {
+		t.Fatal("no failed status write recorded")
+	}
+	if w.ctxErr != nil {
+		t.Fatalf("MarkRunFailed wrote on a cancelled context: %v", w.ctxErr)
+	}
+}
+
+// F5: the per-node worker cap handed to Compute is the run's budget split over
+// the concurrently running nodes.
+func TestLandscapeService_Execute_SplitsWorkerBudgetOverNodes(t *testing.T) {
+	cases := []struct {
+		name string
+		opts LandscapeOptions
+		want int
+	}{
+		{"defaults", LandscapeOptions{}, DefaultMaxWorkers / DefaultMaxConcurrentNodes},
+		{"explicit", LandscapeOptions{MaxWorkers: 12, MaxConcurrentNodes: 3}, 4},
+		{"single node keeps the whole budget", LandscapeOptions{MaxWorkers: 6, MaxConcurrentNodes: 1}, 6},
+		{"never below one", LandscapeOptions{MaxWorkers: 1, MaxConcurrentNodes: 4}, 1},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			f := newLPFixtureWith(t, c.opts)
+			f.seedAllSlots(t)
+			got := f.runOnce(t, RunInput{})
+			if got.Status != domain.LPRunSucceeded {
+				t.Fatalf("run status = %s: %v", got.Status, got.Error)
+			}
+			f.compute.mu.Lock()
+			defer f.compute.mu.Unlock()
+			if len(f.compute.calls) == 0 {
+				t.Fatal("compute was never called")
+			}
+			for _, call := range f.compute.calls {
+				if call.workers != c.want {
+					t.Fatalf("node %s got workers=%d, want %d", call.node, call.workers, c.want)
+				}
+			}
+		})
+	}
+}
+
+// F6: a failing node cancels its siblings instead of letting them run on.
+func TestLandscapeService_Execute_FailingNodeCancelsSiblings(t *testing.T) {
+	// Four stage-0 nodes, all in flight at once; "00" fails immediately while
+	// "01" blocks waiting for its context.
+	f := newLPFixtureWith(t, LandscapeOptions{MaxWorkers: 8, MaxConcurrentNodes: 4})
+	f.seedAllSlots(t)
+	f.compute.errs["00"] = errors.New("boom")
+	f.compute.waitForCancel["01"] = true
+
+	got := f.runOnce(t, RunInput{})
+	if got.Status != domain.LPRunFailed {
+		t.Fatalf("run status = %s, want failed", got.Status)
+	}
+	if !f.compute.observedCancel("01") {
+		t.Fatal("sibling node 01 did not observe the cancellation of its context")
+	}
+	for _, n := range got.Nodes {
+		if n.NodeCode == "01" && n.Status == domain.LPNodeSucceeded {
+			t.Fatal("cancelled sibling must not be recorded as succeeded")
+		}
+	}
+}
+
+// F5: a legacy ComputeFunc still wires up through NewLandscapeService.
+func TestNewLandscapeService_WrapsLegacyComputeFunc(t *testing.T) {
+	f := newLPFixture(t)
+	f.seedAllSlots(t)
+	// Rebuild the service the production-adjacent way: a legacy ComputeFunc,
+	// no direct field substitution.
+	log := slog.New(slog.NewTextHandler(io.Discard, nil))
+	svc := NewLandscapeService(f.runs, f.datasets, f.groups, f.cats, f.pub, f.store, f.jobs, nil, f.compute.fn, log, LandscapeOptions{})
+
+	run, err := svc.CreateRun(context.Background(), RunInput{})
+	if err != nil {
+		t.Fatalf("CreateRun: %v", err)
+	}
+	if err := svc.Execute(context.Background(), run.ID); err != nil {
+		t.Fatalf("Execute: %v", err)
+	}
+	call, ok := f.compute.callFor("00")
+	if !ok {
+		t.Fatal("legacy ComputeFunc was never called")
+	}
+	if call.workers != -1 {
+		t.Fatalf("legacy ComputeFunc should not see a worker cap, got %d", call.workers)
+	}
+}