diff --git a/v3/@claude-flow/cli/package.json b/v3/@claude-flow/cli/package.json
index 584d07f86a..376e0957ef 100644
--- a/v3/@claude-flow/cli/package.json
+++ b/v3/@claude-flow/cli/package.json
@@ -104,8 +104,10 @@
     "@claude-flow/mcp": "3.0.0-alpha.8",
     "@claude-flow/neural": "3.0.0-alpha.9",
     "@claude-flow/shared": "3.0.0-alpha.7",
+    "@metaharness/router": "^0.3.2",
     "@noble/ed25519": "2.3.0",
     "@ruvector/rabitq-wasm": "0.1.0",
+    "metaharness": "^0.4.1",
     "semver": "7.7.3",
     "sql.js": "^1.13.0",
     "yaml": "^2.8.0"
diff --git a/v3/docs/adr/ADR-321-metaharness-hard-dependency.md b/v3/docs/adr/ADR-321-metaharness-hard-dependency.md
new file mode 100644
index 0000000000..9ea66d191b
--- /dev/null
+++ b/v3/docs/adr/ADR-321-metaharness-hard-dependency.md
@@ -0,0 +1,73 @@
+# ADR-321: Promote metaharness to a hard runtime dependency
+
+- **Status**: Accepted
+- **Date**: 2026-07-27
+- **Supersedes**: ADR-150 §"Architectural constraint" rule #2 (optional-only) and rule #1 (removable) as they apply to `metaharness` and `@metaharness/router`
+- **Related**: ADR-150 (metaharness integration surfaces), ADR-148/149 (router integration)
+
+## Context
+
+ADR-150 established metaharness as a *removable augmentation*: `metaharness`
+and every `@metaharness/*` package MUST live in `optionalDependencies` (never
+`dependencies`), every code path that touches them MUST catch `MODULE_NOT_FOUND`
+and degrade gracefully, and a CI gate (`.github/workflows/no-metaharness-smoke.yml`)
+installs ruflo with `--no-optional` and asserts the plugin fleet still passes.
+
+The project has decided to make metaharness a **hard runtime dependency** so it
+is always installed alongside ruflo rather than being an opt-in the platform may
+skip.
+
+### Material fact (recorded for honesty)
+
+At the time of this decision, the two packages are consumed very differently:
+
+- **`metaharness`** — invoked exclusively via **subprocess** (`npx metaharness …`)
+  from `v3/@claude-flow/cli/src/mcp-tools/metaharness-tools.ts`, which carries
+  **zero static `@metaharness/*` imports**. For these MCP tools a hard dependency
+  changes nothing functionally; they shell out regardless of whether the package
+  is declared. The practical benefit is that the package is present locally, so
+  the first `npx` invocation is a cache hit instead of a fetch.
+- **`@metaharness/router`** — imported statically by `neural-router.ts` behind the
+  `CLAUDE_FLOW_ROUTER_NEURAL=1` triple-gate. This is the one consumer for which a
+  *declared* dependency is load-bearing; it was previously expected to be an
+  `optionalDependency` (ADR-150) though not consistently declared.
+
+## Decision
+
+1. Add to `v3/@claude-flow/cli/package.json` `dependencies`:
+   - `metaharness`: `^0.4.1`
+   - `@metaharness/router`: `^0.3.2`
+2. Remove them from `optionalDependencies` (no dual declaration).
+3. This supersedes ADR-150's optional-only + removable constraints **for these two
+   packages only**. The other three ADR-150 rules still hold where they make sense:
+   - **Graceful degradation** — code paths keep their `MODULE_NOT_FOUND` /
+     subprocess-failure fallbacks. A hard dep should always resolve, but the
+     defensive fallbacks are cheap insurance against a broken install and are NOT
+     removed.
+   - **CI coverage** — `metaharness-ci.yml` still exercises the integration.
+
+## Consequences
+
+- **`no-metaharness-smoke.yml` is neutralized in intent.** `npm install --no-optional`
+  only skips `optionalDependencies`; a hard `dependencies` entry is installed
+  regardless, so the "works without metaharness" smoke test can no longer actually
+  remove metaharness and passes trivially. The workflow is left in place (it still
+  validates the plugin fleet's structural contract) but its ADR-150-rule-#4
+  enforcement no longer applies to these two packages. A follow-up may repurpose or
+  retire it.
+- **Install size / surface grows.** metaharness + `@metaharness/router` (+ their
+  transitives) are now always fetched. Acceptable per the decision.
+- **Version-pin risk.** Both packages are 0.x and ship rapid patches. A breaking
+  change in `@metaharness/router@0.4.x` now breaks a hard-dep install, not just an
+  opt-in path. Mitigation: the caret ranges (`^0.4.1` / `^0.3.2`) stay within the
+  current minor; bump deliberately and re-run `metaharness-ci.yml` on upgrade.
+- **Reversibility.** Moving both entries back to `optionalDependencies` restores the
+  ADR-150 model with no code changes, because the graceful-degradation fallbacks
+  were kept.
+
+## Alternatives considered
+
+- **optionalDependency (ADR-150-compliant).** Zero constraint change, same runtime
+  behavior for the subprocess tools. Rejected per the decision to guarantee presence.
+- **Subprocess-only, no declared dep.** Lowest footprint; the status quo for
+  `metaharness`. Rejected for the same reason.