diff --git a/dsl/extdeps/rust/cargo.dag b/dsl/extdeps/rust/cargo.dag
index 2504efe8301..a5b8b2bed16 100644
--- a/dsl/extdeps/rust/cargo.dag
+++ b/dsl/extdeps/rust/cargo.dag
@@ -10,6 +10,7 @@
 
 module extdeps.cargo
 
+import extdeps.cargo_version { CargoPackageVersion, CargoVersionRequirement }
 import std.types { FilePathParts }
 
 // -- Edition -------------------------------------------------------
@@ -35,11 +36,15 @@ fn rust_edition_str(edition: RustEdition) -> String {
 
 data default_rust_edition: RustEdition = Edition2021
 
+// Minimum cargo for edition 2021 (Cargo Reference: "The edition field").
+// Pinned toolchain stays rust-toolchain.toml — this is the honest floor.
+data min_cargo_version: CargoVersionRequirement = ">= 1.56"
+
 // -- Package model -------------------------------------------------
 
 type CargoPackage {
   name: String
-  version: String
+  version: CargoPackageVersion
   edition: RustEdition
   path: String
 }
@@ -51,7 +56,7 @@ type CargoPackage {
 // version (with optional features); a path dependency points at a local
 // crate directory. (Git/other sources extend this coproduct when needed.)
 type CargoDepSource
-  = RegistryDep  { version: String, features: List<String> }
+  = RegistryDep  { version: CargoVersionRequirement, features: List<String> }
   | LocalPathDep { path: String }
 
 type CargoDependency {
diff --git a/dsl/extdeps/rust/version.dag b/dsl/extdeps/rust/version.dag
new file mode 100644
index 00000000000..a55177d70f0
--- /dev/null
+++ b/dsl/extdeps/rust/version.dag
@@ -0,0 +1,44 @@
+// extdeps/rust/version.dag — Cargo version carriers (SemVer scheme + requirements).
+//
+// Fidelity — extdeps invariant (cite source; DESIGN.md §3):
+//   Spec: https://doc.rust-lang.org/cargo/reference/manifest.html
+//   Package version field: SemVer 2.0.0 (manifest.md#the-version-field).
+//   Dependency version field: semver version requirement
+//   (specifying-dependencies.md#specifying-dependencies) — caret/tilde/comparator
+//   syntax, not a bare published version.
+//
+// Authority: extdeps.version.semver (semver.org), not std.types.SemVer.
+//
+// Consumers:
+//   extdeps/rust/cargo.dag — `CargoPackage`, `RegistryDep`
+
+module extdeps.cargo_version
+
+import extdeps.version.semver { SemVerIdentity, SemVerConstraint }
+
+// Published crate version in `[package].version` (crates.io / workspace manifests).
+type CargoPackageVersion = SemVerIdentity
+
+// Dependency version requirement in `[dependencies].crate = "…"`.
+type CargoVersionRequirement = SemVerConstraint
+
+// Single authority for the stage0/bootstrap crate package version token.
+data default_stage0_package_version: CargoPackageVersion = "0.1.0"
+
+// Render helpers exercised by witnesses (manifest emission reuses these tokens).
+fn render_cargo_package_version_field(version: CargoPackageVersion) -> String {
+  concat("version = \"", version, "\"")
+}
+
+fn render_cargo_version_requirement_toml(req: CargoVersionRequirement) -> String {
+  concat("\"", req, "\"")
+}
+
+// `[package]` header through default_stage0_package_version — shared by
+// `stage0_crates.emit_stage0_crate_manifest` and `emit_rust.emit_cargo_toml`.
+fn render_cargo_package_header_prefix(name: String) -> String {
+  concat(
+    "[package]\nname = \"", name, "\"\n",
+    render_cargo_package_version_field(version: default_stage0_package_version)
+  )
+}
diff --git a/dsl/extdeps/version/semver.dag b/dsl/extdeps/version/semver.dag
new file mode 100644
index 00000000000..b22eae27c45
--- /dev/null
+++ b/dsl/extdeps/version/semver.dag
@@ -0,0 +1,30 @@
+// extdeps/version/semver.dag — Semantic Versioning scheme (slice 2).
+//
+// Spec: https://semver.org/
+//
+// Inhabits extdeps.version carriers — not std.types.SemVer (String alias; OCI migration
+// is a separate escalation-gated PR). Ecosystem consumers (Cargo package version, etc.)
+// import SemVerIdentity / SemVerConstraint from here.
+//
+// Structured MAJOR.MINOR.PATCH decomposition and semver-aware ordering land in slice-2b;
+// semver_scheme below uses wire-label equality until then (dissolve-on).
+
+module extdeps.version.semver
+
+import extdeps.version { VersionIdentity, VersionScheme, VersionConstraint }
+import std.algebra { Ordering, Less, Equal, Greater }
+
+// Published semver version label (MAJOR.MINOR.PATCH wire form).
+type SemVerIdentity = VersionIdentity
+
+// Semver version requirement / comparator wire text — not a published identity.
+type SemVerConstraint = VersionConstraint
+
+// Interim compare: equality on wire labels only (slice-2b adds semver-aware ordering).
+fn semver_identity_compare(a: VersionIdentity, b: VersionIdentity) -> Ordering {
+  if a == b { Equal } else { if a < b { Less } else { Greater } }
+}
+
+data semver_scheme: VersionScheme = {
+  compare: semver_identity_compare
+}
diff --git a/dsl/std/realization_width.dag b/dsl/std/realization_width.dag
index cc21c92b118..d2447b8c4f0 100644
--- a/dsl/std/realization_width.dag
+++ b/dsl/std/realization_width.dag
@@ -23,9 +23,12 @@ module std.realization_width
 import std.types { Int, List }
 import std.measure {
   HardwareThreadCount,
-  NanosecondDuration,
   hardware_thread_count,
   hardware_thread_count_value,
+  Nano,
+}
+import std.verification {
+  NanosecondDuration,
   nanosecond_duration,
 }
 import std.pareto { AxisGoal, LowerIsBetter }
@@ -38,7 +41,7 @@ import std.realization_schedule {
   schedule_eq,
   cost_account_measured,
   cost_account_predicted_zero,
-  cost_account_time_nanos,
+  cost_account_time_count,
 }
 
 fn int_min(a: Int, b: Int) -> Int {
@@ -72,13 +75,13 @@ fn width_fold_objective_goals() -> List<AxisGoal> {
 }
 
 type WidthBoundedRealization {
-  plan: RealizationPlan
+  plan: RealizationPlan<Nano>
   spawn_width: HardwareThreadCount
 }
 
 // Width is peripheral: the schedule topology is unchanged (§3 invariant).
 fn width_bounded_realization(
-  plan: RealizationPlan,
+  plan: RealizationPlan<Nano>,
   shard_count: Int,
   hardware_threads: HardwareThreadCount
 ) -> WidthBoundedRealization {
@@ -89,7 +92,7 @@ fn width_bounded_realization(
 }
 
 fn witness_width_fold_preserves_schedule_topology(
-  plan: RealizationPlan,
+  plan: RealizationPlan<Nano>,
   shard_count: Int,
   hardware_threads: HardwareThreadCount
 ) -> Bool {
@@ -123,10 +126,10 @@ fn witness_budget_ignoring_fold_fails(
 }
 
 // Measured shard-balance scaffold: assignment must read CostAccount.basis=Measured.
-fn shard_balance_slot_for_cost(cost: CostAccount, baseline: CostAccount) -> Int {
+fn shard_balance_slot_for_cost(cost: CostAccount<Nano>, baseline: CostAccount<Nano>) -> Int {
   match cost.basis {
-    Measured => cost_account_time_nanos(account: cost)
-    Predicted => cost_account_time_nanos(account: baseline)
+    Measured => cost_account_time_count(account: cost)
+    Predicted => cost_account_time_count(account: baseline)
   }
 }
 
diff --git a/dsl/test/claim/cargo_version_witness_test.dag b/dsl/test/claim/cargo_version_witness_test.dag
new file mode 100644
index 00000000000..ad513a534c8
--- /dev/null
+++ b/dsl/test/claim/cargo_version_witness_test.dag
@@ -0,0 +1,76 @@
+// test/claim/cargo_version_witness_test.dag — by-execution witness for Cargo SemVer carriers.
+//
+// DESIGN §5 green-by-execution: `CargoPackageVersion` and `CargoVersionRequirement`
+// are not spec-without-execution — this witness folds render helpers and the stage0
+// default over discriminating inputs. Reverting either field to bare `String` or
+// dropping the branded requirement carrier breaks the typed data rows below.
+
+module test.claim.cargo_version
+
+import extdeps.cargo {
+  CargoPackage,
+  CargoDependency,
+  RegistryDep,
+  Edition2021,
+  min_cargo_version,
+}
+import extdeps.cargo_version {
+  default_stage0_package_version,
+  render_cargo_package_version_field,
+  render_cargo_package_header_prefix,
+  render_cargo_version_requirement_toml,
+}
+
+fn w_stage0_default_package_version() -> Bool {
+  default_stage0_package_version == "0.1.0"
+    && render_cargo_package_version_field(version: default_stage0_package_version) == "version = \"0.1.0\""
+}
+
+fn w_package_version_field_renders() -> Bool {
+  let pkg = CargoPackage {
+    name: "demo",
+    version: "2.4.6",
+    edition: Edition2021,
+    path: "."
+  }
+  render_cargo_package_version_field(version: pkg.version) == "version = \"2.4.6\""
+}
+
+fn w_registry_dep_version_requirements() -> Bool {
+  let serde = CargoDependency {
+    name: "serde",
+    source: RegistryDep { version: "1", features: ["derive", "rc"] }
+  }
+  let stacker = CargoDependency {
+    name: "stacker",
+    source: RegistryDep { version: "0.1", features: [] }
+  }
+  match serde.source {
+    RegistryDep { version: v, features: f } =>
+      render_cargo_version_requirement_toml(req: v) == "\"1\""
+        && (f |> count) == 2
+    LocalPathDep { path: _ } => false
+  }
+    && match stacker.source {
+      RegistryDep { version: v, features: f } =>
+        render_cargo_version_requirement_toml(req: v) == "\"0.1\""
+          && (f |> count) == 0
+      LocalPathDep { path: _ } => false
+    }
+}
+
+fn w_requirement_distinct_from_package_version() -> Bool {
+  render_cargo_version_requirement_toml(req: "1") != render_cargo_package_version_field(version: "1.0.0")
+}
+
+fn w_emitter_header_prefix_uses_default() -> Bool {
+  render_cargo_package_header_prefix(name: "demo-crate") == "[package]\nname = \"demo-crate\"\nversion = \"0.1.0\""
+}
+
+test fn cargo_version_witnesses() -> Bool {
+  w_stage0_default_package_version()
+    && w_package_version_field_renders()
+    && w_registry_dep_version_requirements()
+    && w_requirement_distinct_from_package_version()
+    && w_emitter_header_prefix_uses_default()
+}
diff --git a/dsl/test/claim/extdeps_version_semver_witness_test.dag b/dsl/test/claim/extdeps_version_semver_witness_test.dag
new file mode 100644
index 00000000000..82b9753ef43
--- /dev/null
+++ b/dsl/test/claim/extdeps_version_semver_witness_test.dag
@@ -0,0 +1,38 @@
+// By-execution witnesses for extdeps.version.semver (slice 2).
+//
+// Run via:
+//   gunbc run --source-root dsl --entry dsl/test/claim/extdeps_version_semver_witness_test.dag \
+//     --function extdeps_version_semver_witnesses --claim-run
+
+module test.claim.extdeps_version_semver
+
+import extdeps.version.semver { SemVerIdentity, SemVerConstraint, semver_scheme }
+import std.algebra { Equal }
+
+fn semver_identity_1_2_3() -> SemVerIdentity { "1.2.3" }
+fn semver_constraint_caret() -> SemVerConstraint { "^1.2" }
+fn semver_identity_1_0_0() -> SemVerIdentity { "1.0.0" }
+fn semver_constraint_one() -> SemVerConstraint { "1" }
+
+fn w_semver_identity_inhabits_version_identity() -> Bool {
+  semver_identity_1_2_3() == "1.2.3"
+}
+
+fn w_semver_constraint_inhabits_version_constraint() -> Bool {
+  semver_constraint_caret() == "^1.2"
+}
+
+fn w_identity_distinct_from_constraint() -> Bool {
+  semver_identity_1_0_0() != semver_constraint_one()
+}
+
+fn w_semver_scheme_equality_compare() -> Bool {
+  semver_scheme.compare("1.0.0", "1.0.0") == Equal
+}
+
+test fn extdeps_version_semver_witnesses() -> Bool {
+  w_semver_identity_inhabits_version_identity()
+    && w_semver_constraint_inhabits_version_constraint()
+    && w_identity_distinct_from_constraint()
+    && w_semver_scheme_equality_compare()
+}
diff --git a/dsl/test/claim/realization_width_witness_test.dag b/dsl/test/claim/realization_width_witness_test.dag
index 0deadafb09a..8cdfda90144 100644
--- a/dsl/test/claim/realization_width_witness_test.dag
+++ b/dsl/test/claim/realization_width_witness_test.dag
@@ -34,7 +34,7 @@ fn witness_threads_4() -> HardwareThreadCount {
   hardware_thread_count(4)
 }
 
-fn synthetic_plan() -> RealizationPlan {
+fn synthetic_plan() -> RealizationPlan<Nano> {
   RealizationPlan {
     target: "width-witness-target"
     objective: RealizationObjective { goals: [] }
diff --git a/src/v1/05_emit_rust.dag b/src/v1/05_emit_rust.dag
index a86ee4196d1..987521ebdcb 100644
--- a/src/v1/05_emit_rust.dag
+++ b/src/v1/05_emit_rust.dag
@@ -71,6 +71,7 @@ import extdeps.languages.rust.emit {
   rust_serde_rename_all_snake_case, rust_serde_rename_all_screaming_snake_case,
   HigherOrderMethodSpec, rust_higher_order_methods
 }
+import extdeps.cargo_version { render_cargo_package_header_prefix }
 import v1.compiler.languages {
   scaffold_for_target, serialization_for_target,
   TestConventions, ItemKeywords,
@@ -7511,7 +7512,7 @@ fn emit_cargo_dep(name: String, version: String, features: List<String>) -> Stri
 }
 
 fn emit_cargo_toml(crate_name: String, has_services: Bool) -> TextFile {
-  let header = concat("[package]\nname = \"", crate_name, "\"\nversion = \"0.1.0\"\nedition = \"2021\"\n")
+  let header = concat(render_cargo_package_header_prefix(name: crate_name), "\nedition = \"2021\"\n")
   let workspace = "\n[workspace]\n"
   let base_deps = [
     emit_cargo_dep(name: "serde", version: "1", features: ["derive", "rc"]),
diff --git a/src/v1/stage0_crates.dag b/src/v1/stage0_crates.dag
index 06e475df82f..c30c73f42bf 100644
--- a/src/v1/stage0_crates.dag
+++ b/src/v1/stage0_crates.dag
@@ -22,6 +22,7 @@ module v1.compiler.stage0_crates
 import v1.std.core { TextFile }
 import v1.compiler.emit_rust { emit_non_empty_wrappers, emit_cargo_dep }
 import extdeps.cargo { CargoDependency, CargoFeature, RegistryDep, LocalPathDep }
+import extdeps.cargo_version { render_cargo_package_header_prefix }
 
 // =========================================================================
 // Crate-boundary model
@@ -155,7 +156,8 @@ fn render_stage0_crate_features_section(features: List<CargoFeature>) -> String
 fn emit_stage0_crate_manifest(spec: Stage0CrateSpec) -> TextFile {
   let deps = spec.dependencies |> map(render_stage0_crate_dep) |> join(separator: "")
   let content = concat(
-    "[package]\nname = \"", spec.package_name, "\"\nversion = \"0.1.0\"\nedition = \"2021\"",
+    render_cargo_package_header_prefix(name: spec.package_name),
+    "\nedition = \"2021\"",
     render_stage0_crate_features_section(features: spec.features),
     "\n\n[dependencies]\n",
     deps