diff --git a/internal/agent/loop.go b/internal/agent/loop.go
index e6c700864..44701588b 100644
--- a/internal/agent/loop.go
+++ b/internal/agent/loop.go
@@ -632,10 +632,9 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 			// The scan happens lazily at the run's first index — never ahead of a
 			// pending mutating call — so read-after-write ordering is preserved.
 			if index >= precomputedEnd {
-				runEnd := index
-				for runEnd < len(collected.ToolCalls) && parallelSafeToolCall(registry, collected.ToolCalls[runEnd], options) {
-					runEnd++
-				}
+				// Capability-safe consecutive run (ReadOnly+ThreadSafe, no
+				// resource-key conflicts). See extendParallelRun.
+				runEnd := extendParallelRun(registry, collected.ToolCalls, index, options)
 				if runEnd-index >= 2 {
 					batchSpan := options.Trace.Span(trace.SpanToolExecution)
 					precomputed = executeParallelReadBatch(ctx, registry, collected.ToolCalls, index, runEnd, permissionMode, options)
diff --git a/internal/agent/parallel_tools.go b/internal/agent/parallel_tools.go
index 48e5960dd..11d6e28a3 100644
--- a/internal/agent/parallel_tools.go
+++ b/internal/agent/parallel_tools.go
@@ -10,12 +10,23 @@ import (
 // Parallel read-ahead for tool batches. When a turn requests several
 // independent lookups (read_file + grep + glob is the common shape), executing
 // them one after another serializes pure I/O waits. A consecutive run of
-// auto-allowed read-only calls is executed concurrently instead; results are
+// capability-safe read-only calls is executed concurrently instead; results are
 // then consumed in the original call order, so guard counters, message
 // ordering, abort semantics, and the surface's call/result event pairing are
 // byte-identical to sequential execution. Runs never span a mutating call: a
 // read that follows a write must observe the write, so eligibility is decided
 // per consecutive run, not per batch.
+//
+// Eligibility uses the PR5 tool-effect contract (tools.CapabilitiesOf):
+//
+//	Effect == ReadOnly
+//	AND ThreadSafe == true
+//	AND auto-allowed (no interactive permission prompt on the hot path)
+//	AND no resource-key conflict with an earlier call in the same concurrent window
+//
+// Unknown, mutators, interactive tools, and non-thread-safe reads stay
+// sequential. Empty resource keys do not conflict (ThreadSafe is the safety
+// gate); shared non-empty keys force a batch boundary.
 
 // maxParallelReadTools bounds concurrent read-only tool executions in a turn.
 const maxParallelReadTools = 8
@@ -28,26 +39,115 @@ type precomputedToolResult struct {
 }
 
 // parallelSafeToolCall reports whether call may run concurrently with its
-// neighbors: the tool must exist, be side-effect-free (SideEffectRead), and be
-// auto-allowed for these args, so no interactive prompt or workspace mutation
-// is on the hot path. Loop-intercepted tools (ask_user, request_permissions)
-// and tool_search (mutates the deferred-tool set) stay sequential.
+// neighbors under the PR5 capability contract. Loop-intercepted tools
+// (ask_user, request_permissions) and tool_search (mutates the deferred-tool
+// set) always stay sequential.
 func parallelSafeToolCall(registry *tools.Registry, call ToolCall, options Options) bool {
 	switch call.Name {
 	case "ask_user", tools.RequestPermissionsToolName, tools.ToolSearchToolName:
 		return false
 	}
 	tool, found := registry.Get(call.Name)
-	if !found || tool.Safety().SideEffect != tools.SideEffectRead {
+	if !found {
 		return false
 	}
+	caps := tools.CapabilitiesOf(tool)
+	// Fail-closed: only audited concurrent-safe pure reads.
+	if caps.Effect != tools.EffectReadOnly || !caps.ThreadSafe {
+		return false
+	}
+	args, ok := decodeCallArgs(call)
+	if !ok {
+		return false
+	}
+	return effectivePermission(tool, args) == tools.PermissionAllow
+}
+
+// decodeCallArgs decodes tool call JSON arguments. Returns false on malformed
+// input so the call stays sequential (never panics into the parallel path).
+func decodeCallArgs(call ToolCall) (map[string]any, bool) {
 	args := map[string]any{}
-	if call.Arguments != "" {
-		if err := decodeToolArguments(call.Arguments, &args); err != nil {
-			return false
+	if call.Arguments == "" {
+		return args, true
+	}
+	if err := decodeToolArguments(call.Arguments, &args); err != nil {
+		return nil, false
+	}
+	return args, true
+}
+
+// resourceKeysForCall returns the conflict keys for a call, or nil when the
+// tool has no ResourceKeys function / no keys for these args.
+func resourceKeysForCall(registry *tools.Registry, call ToolCall) []string {
+	tool, found := registry.Get(call.Name)
+	if !found {
+		return nil
+	}
+	caps := tools.CapabilitiesOf(tool)
+	if caps.ResourceKeys == nil {
+		return nil
+	}
+	args, ok := decodeCallArgs(call)
+	if !ok {
+		return nil
+	}
+	return caps.ResourceKeys(args)
+}
+
+// resourceKeysConflict reports whether two key sets share any non-empty key.
+// Empty key sets never conflict: ThreadSafe is the eligibility gate; keys only
+// refine conflict detection among tools that declare specific resources.
+func resourceKeysConflict(a, b []string) bool {
+	if len(a) == 0 || len(b) == 0 {
+		return false
+	}
+	seen := make(map[string]struct{}, len(a))
+	for _, key := range a {
+		if key == "" {
+			continue
 		}
+		seen[key] = struct{}{}
 	}
-	return effectivePermission(tool, args) == tools.PermissionAllow
+	for _, key := range b {
+		if key == "" {
+			continue
+		}
+		if _, ok := seen[key]; ok {
+			return true
+		}
+	}
+	return false
+}
+
+// extendParallelRun returns the exclusive end index of a consecutive parallel-
+// safe run starting at start. The run stops before the first call that is not
+// parallel-safe or that conflicts on resource keys with any earlier call in
+// the same window (so two read_file calls on the same path stay sequential).
+func extendParallelRun(registry *tools.Registry, calls []ToolCall, start int, options Options) int {
+	if start >= len(calls) || !parallelSafeToolCall(registry, calls[start], options) {
+		return start
+	}
+	end := start + 1
+	keysWindow := [][]string{resourceKeysForCall(registry, calls[start])}
+	for end < len(calls) {
+		if !parallelSafeToolCall(registry, calls[end], options) {
+			break
+		}
+		nextKeys := resourceKeysForCall(registry, calls[end])
+		conflict := false
+		for _, prev := range keysWindow {
+			if resourceKeysConflict(prev, nextKeys) {
+				conflict = true
+				break
+			}
+		}
+		if conflict {
+			break
+		}
+		keysWindow = append(keysWindow, nextKeys)
+		end++
+	}
+	return end
 }
 
 // executeParallelReadBatch runs calls[start:end] concurrently (bounded by
diff --git a/internal/agent/parallel_tools_test.go b/internal/agent/parallel_tools_test.go
index 411783958..4a355e7d5 100644
--- a/internal/agent/parallel_tools_test.go
+++ b/internal/agent/parallel_tools_test.go
@@ -57,6 +57,20 @@ func (tool *probeTool) Parameters() tools.Schema {
 func (tool *probeTool) Safety() tools.Safety {
 	return tools.Safety{SideEffect: tool.sideEffect, Permission: tools.PermissionAllow, Reason: "test"}
 }
+
+// Capabilities maps the probe's SideEffect into the PR5 capability contract so
+// parallelSafeToolCall (CapabilitiesOf) can classify reads vs mutators. Without
+// this, probes default to EffectUnknown and never enter the concurrent path.
+func (tool *probeTool) Capabilities() tools.ToolCapabilities {
+	switch tool.sideEffect {
+	case tools.SideEffectRead:
+		return tools.ToolCapabilities{Effect: tools.EffectReadOnly, ThreadSafe: true}
+	case tools.SideEffectWrite:
+		return tools.ToolCapabilities{Effect: tools.EffectWorkspaceWrite, ThreadSafe: false}
+	default:
+		return tools.UnknownCapabilities()
+	}
+}
 func (tool *probeTool) Run(_ context.Context, args map[string]any) tools.Result {
 	id, _ := args["id"].(string)
 	tool.mu.Lock()
@@ -92,6 +106,11 @@ func TestParallelSafeToolCall(t *testing.T) {
 	registry := tools.NewRegistry()
 	registry.Register(&probeTool{name: "probe_read", sideEffect: tools.SideEffectRead})
 	registry.Register(&probeTool{name: "probe_write", sideEffect: tools.SideEffectWrite})
+	// Read-only but not ThreadSafe: must stay sequential under the PR5 gate.
+	registry.Register(&keyedProbeTool{
+		probeTool:  probeTool{name: "probe_read_serial", sideEffect: tools.SideEffectRead},
+		threadSafe: false,
+	})
 
 	call := func(name, args string) ToolCall { return ToolCall{ID: "c", Name: name, Arguments: args} }
 	if !parallelSafeToolCall(registry, call("probe_read", `{"id":"a"}`), Options{}) {
@@ -109,6 +128,91 @@ func TestParallelSafeToolCall(t *testing.T) {
 	if parallelSafeToolCall(registry, call("ask_user", `{}`), Options{}) {
 		t.Fatal("loop-intercepted tools must stay sequential")
 	}
+	if parallelSafeToolCall(registry, call("probe_read_serial", `{"id":"a"}`), Options{}) {
+		t.Fatal("ReadOnly without ThreadSafe must not be parallel-safe")
+	}
+}
+
+func TestResourceKeysConflict(t *testing.T) {
+	if resourceKeysConflict(nil, []string{"file:a"}) {
+		t.Fatal("empty vs non-empty must not conflict")
+	}
+	if resourceKeysConflict([]string{"file:a"}, nil) {
+		t.Fatal("non-empty vs empty must not conflict")
+	}
+	if resourceKeysConflict([]string{"file:a"}, []string{"file:b"}) {
+		t.Fatal("distinct keys must not conflict")
+	}
+	if !resourceKeysConflict([]string{"file:a", "file:b"}, []string{"file:b"}) {
+		t.Fatal("shared key must conflict")
+	}
+	if resourceKeysConflict([]string{"", "file:a"}, []string{""}) {
+		t.Fatal("empty-string keys must be ignored")
+	}
+}
+
+func TestExtendParallelRunResourceKeyBoundary(t *testing.T) {
+	// Two keyed reads on the same path must not share a concurrent window;
+	// distinct paths may batch together.
+	registry := tools.NewRegistry()
+	registry.Register(&keyedProbeTool{
+		probeTool:  probeTool{name: "keyed_read", sideEffect: tools.SideEffectRead},
+		threadSafe: true,
+		keys: func(args map[string]any) []string {
+			id, _ := args["id"].(string)
+			if id == "" {
+				return nil
+			}
+			return []string{"file:" + id}
+		},
+	})
+	calls := []ToolCall{
+		{ID: "1", Name: "keyed_read", Arguments: `{"id":"a"}`},
+		{ID: "2", Name: "keyed_read", Arguments: `{"id":"b"}`},
+		{ID: "3", Name: "keyed_read", Arguments: `{"id":"a"}`}, // conflicts with call 0
+	}
+	// start=0: a and b share no key → run covers [0,2)
+	if end := extendParallelRun(registry, calls, 0, Options{}); end != 2 {
+		t.Fatalf("extend from 0 = %d, want 2 (stop before second file:a)", end)
+	}
+	// start=2: single remaining call
+	if end := extendParallelRun(registry, calls, 2, Options{}); end != 3 {
+		t.Fatalf("extend from 2 = %d, want 3", end)
+	}
+	// Empty keys never conflict: three keyless safe reads form one window.
+	registry.Register(&probeTool{name: "keyless_read", sideEffect: tools.SideEffectRead})
+	keyless := []ToolCall{
+		{ID: "1", Name: "keyless_read", Arguments: `{"id":"x"}`},
+		{ID: "2", Name: "keyless_read", Arguments: `{"id":"y"}`},
+		{ID: "3", Name: "keyless_read", Arguments: `{"id":"z"}`},
+	}
+	if end := extendParallelRun(registry, keyless, 0, Options{}); end != 3 {
+		t.Fatalf("keyless extend = %d, want 3", end)
+	}
+}
+
+// keyedProbeTool is a probe with explicit ResourceKeys / ThreadSafe for
+// planner unit tests.
+type keyedProbeTool struct {
+	probeTool
+	threadSafe bool
+	keys       func(args map[string]any) []string
+}
+
+func (tool *keyedProbeTool) Capabilities() tools.ToolCapabilities {
+	caps := tools.ToolCapabilities{
+		Effect:     tools.EffectReadOnly,
+		ThreadSafe: tool.threadSafe,
+	}
+	if tool.keys != nil {
+		caps.ResourceKeys = tool.keys
+	}
+	// Honor mutator side effects from the embedded probe when used as write.
+	if tool.sideEffect == tools.SideEffectWrite {
+		caps.Effect = tools.EffectWorkspaceWrite
+		caps.ThreadSafe = false
+	}
+	return caps
 }
 
 func TestRunExecutesConsecutiveReadsConcurrently(t *testing.T) {
diff --git a/internal/tools/capabilities_test.go b/internal/tools/capabilities_test.go
index cfb422253..0a6c0a048 100644
--- a/internal/tools/capabilities_test.go
+++ b/internal/tools/capabilities_test.go
@@ -300,6 +300,18 @@ func TestInteractiveClassifications(t *testing.T) {
 
 func TestReadOnlyClassifications(t *testing.T) {
 	root := t.TempDir()
+	// PR6 audited concurrent-safe pure reads (mutex-guarded FileTracker,
+	// independent scan I/O, independent HTTP). Others stay sequential until
+	// their shared state is proven safe under concurrent Run.
+	threadSafeReads := map[string]bool{
+		"read_file":          true,
+		"read_minified_file": true,
+		"list_directory":     true,
+		"glob":               true,
+		"grep":               true,
+		"skill":              true,
+		"web_fetch":          true,
+	}
 	for _, name := range []string{"read_file", "read_minified_file", "list_directory", "glob", "grep", "lsp_navigate", "skill", "web_fetch", "web_search", "tool_search"} {
 		var found Tool
 		for _, tool := range BuiltinCatalog(root) {
@@ -315,14 +327,38 @@ func TestReadOnlyClassifications(t *testing.T) {
 		if caps.Effect != EffectReadOnly {
 			t.Errorf("%s effect = %v, want ReadOnly", name, caps.Effect)
 		}
-		// Current catalog intentionally keeps read tools non-thread-safe
-		// until each is audited for shared mutable state (FileTracker, etc.).
-		if caps.ThreadSafe {
-			t.Errorf("%s ThreadSafe=true without explicit audit", name)
+		wantSafe := threadSafeReads[name]
+		if caps.ThreadSafe != wantSafe {
+			t.Errorf("%s ThreadSafe=%v, want %v", name, caps.ThreadSafe, wantSafe)
 		}
 	}
 }
 
+func TestScopedScanResourceKeys(t *testing.T) {
+	// Workspace-wide scan → no keys (do not false-conflict every concurrent scan).
+	if keys := scopedScanResourceKeys(nil); keys != nil {
+		t.Fatalf("nil args = %v, want nil", keys)
+	}
+	if keys := scopedScanResourceKeys(map[string]any{}); keys != nil {
+		t.Fatalf("empty args = %v, want nil", keys)
+	}
+	if keys := scopedScanResourceKeys(map[string]any{"cwd": "."}); keys != nil {
+		t.Fatalf("cwd=. = %v, want nil", keys)
+	}
+	if keys := scopedScanResourceKeys(map[string]any{"path": "."}); keys != nil {
+		t.Fatalf("path=. = %v, want nil", keys)
+	}
+	// Scoped path → directory: key (glob uses cwd; grep uses path).
+	keys := scopedScanResourceKeys(map[string]any{"cwd": "internal/tools"})
+	if len(keys) != 1 || keys[0] != ResourceKeyDirectory+NormalizeResourcePath("internal/tools") {
+		t.Fatalf("cwd scoped = %v", keys)
+	}
+	keys = scopedScanResourceKeys(map[string]any{"path": "./pkg/../pkg/api"})
+	if len(keys) != 1 || keys[0] != ResourceKeyDirectory+NormalizeResourcePath("./pkg/../pkg/api") {
+		t.Fatalf("path scoped = %v", keys)
+	}
+}
+
 func TestValidateBuiltinCatalogRejectsUnknownRaw(t *testing.T) {
 	// Prove the gate is not a rubber stamp: raw Unknown+ThreadSafe is rejected.
 	problems := ValidateCapabilities("ghost", ToolCapabilities{Effect: EffectUnknown, ThreadSafe: true})
diff --git a/internal/tools/glob.go b/internal/tools/glob.go
index e36400c84..b54462abc 100644
--- a/internal/tools/glob.go
+++ b/internal/tools/glob.go
@@ -39,7 +39,7 @@ func NewScopedGlobTool(workspaceRoot string, scope PathScope) Tool {
 				AdditionalProperties: false,
 			},
 			safety:       readOnlySafety("Finds matching paths without reading contents or modifying files."),
-			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: false, ResourceKeys: workspaceResourceKeys},
+			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: true, ResourceKeys: scopedScanResourceKeys},
 		},
 		workspaceRoot: normalizeWorkspaceRoot(workspaceRoot),
 		scope:         scope,
diff --git a/internal/tools/grep.go b/internal/tools/grep.go
index 6ffe22356..8827bb619 100644
--- a/internal/tools/grep.go
+++ b/internal/tools/grep.go
@@ -54,7 +54,7 @@ func NewScopedGrepTool(workspaceRoot string, scope PathScope) Tool {
 				AdditionalProperties: false,
 			},
 			safety:       readOnlySafety("Searches file paths and matching lines without modifying files."),
-			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: false, ResourceKeys: workspaceResourceKeys},
+			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: true, ResourceKeys: scopedScanResourceKeys},
 		},
 		workspaceRoot: normalizeWorkspaceRoot(workspaceRoot),
 		scope:         scope,
diff --git a/internal/tools/list_directory.go b/internal/tools/list_directory.go
index f03cfa9fe..429cf948b 100644
--- a/internal/tools/list_directory.go
+++ b/internal/tools/list_directory.go
@@ -34,7 +34,7 @@ func NewScopedListDirectoryTool(workspaceRoot string, scope PathScope) Tool {
 				AdditionalProperties: false,
 			},
 			safety:       readOnlySafety("Lists directory entries without modifying files."),
-			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: false, ResourceKeys: directoryResourceKeys},
+			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: true, ResourceKeys: directoryResourceKeys},
 		},
 		workspaceRoot: normalizeWorkspaceRoot(workspaceRoot),
 		scope:         scope,
diff --git a/internal/tools/read_file.go b/internal/tools/read_file.go
index 02ad04559..15e3d1abe 100644
--- a/internal/tools/read_file.go
+++ b/internal/tools/read_file.go
@@ -39,8 +39,10 @@ func NewScopedReadFileTool(workspaceRoot string, scope PathScope) Tool {
 				AdditionalProperties: false,
 			},
 			safety: readOnlySafety("Reads file contents without modifying files."),
-			// ThreadSafe=false: may update FileTracker session state on read.
-			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: false, ResourceKeys: fileResourceKeys},
+			// ThreadSafe: FileTracker is mutex-guarded; concurrent reads of
+			// distinct paths are safe. Same-path calls still serialize via
+			// resource-key conflict detection in the agent parallel planner.
+			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: true, ResourceKeys: fileResourceKeys},
 		},
 		workspaceRoot: normalizeWorkspaceRoot(workspaceRoot),
 		scope:         scope,
diff --git a/internal/tools/read_minified_file.go b/internal/tools/read_minified_file.go
index 1b6e98994..beacd5986 100644
--- a/internal/tools/read_minified_file.go
+++ b/internal/tools/read_minified_file.go
@@ -34,7 +34,7 @@ func NewScopedReadMinifiedFileTool(workspaceRoot string, scope PathScope) Tool {
 				AdditionalProperties: false,
 			},
 			safety:       readOnlySafety("Reads a minified view of file contents without modifying files."),
-			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: false, ResourceKeys: fileResourceKeys},
+			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: true, ResourceKeys: fileResourceKeys},
 		},
 		workspaceRoot: normalizeWorkspaceRoot(workspaceRoot),
 		scope:         scope,
diff --git a/internal/tools/resource_keys.go b/internal/tools/resource_keys.go
index 20e0c9015..a232efd99 100644
--- a/internal/tools/resource_keys.go
+++ b/internal/tools/resource_keys.go
@@ -127,6 +127,20 @@ func workspaceResourceKeys(_ map[string]any) []string {
 	return []string{ResourceKeyWorkspace + "root"}
 }
 
+// scopedScanResourceKeys returns conflict keys for directory-scoped scan tools
+// (glob, grep). Workspace-wide scans (missing / empty / ".") return nil so
+// they do not force a false conflict with every other concurrent scan —
+// ThreadSafe is the concurrency gate; keys refine same-directory collisions.
+// A non-default path/cwd yields a single directory: key.
+func scopedScanResourceKeys(args map[string]any) []string {
+	path := firstStringArg(args, "path", "cwd", "dir", "directory")
+	normalized := NormalizeResourcePath(path)
+	if normalized == "" || normalized == "." {
+		return nil
+	}
+	return []string{ResourceKeyDirectory + normalized}
+}
+
 // multiFileResourceKeys collects path and paths[] arguments into file: keys.
 func multiFileResourceKeys(args map[string]any) []string {
 	var keys []string
diff --git a/internal/tools/skill.go b/internal/tools/skill.go
index 27367d959..0238974d0 100644
--- a/internal/tools/skill.go
+++ b/internal/tools/skill.go
@@ -49,7 +49,7 @@ func NewSkillTool(dir string) *skillTool {
 				AdditionalProperties: false,
 			},
 			safety:       readOnlySafety("Reads a local skill file; gathers reusable instructions only."),
-			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: false},
+			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: true},
 		},
 	}
 }
diff --git a/internal/tools/web_fetch.go b/internal/tools/web_fetch.go
index f4c18ef0e..be3fe90e9 100644
--- a/internal/tools/web_fetch.go
+++ b/internal/tools/web_fetch.go
@@ -141,8 +141,11 @@ func newWebFetchToolWithClientAndResolver(client *http.Client, resolver webFetch
 				Reason:          "Fetches remote URL content over the network.",
 				AdvertiseInAuto: true,
 			},
-			// Network read; ThreadSafe=false until client proven concurrent-safe.
-			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: false, ResourceKeys: endpointResourceKeys},
+			// Concurrent-safe: net/http.Client is documented as safe for
+			// concurrent use; each call issues independent request I/O.
+			// parallelSafeToolCall still requires PermissionAllow (prompted
+			// network fetches stay sequential until auto-allowed).
+			capabilities: ToolCapabilities{Effect: EffectReadOnly, ThreadSafe: true, ResourceKeys: endpointResourceKeys},
 		},
 		client:   client,
 		resolver: resolver,