diff --git a/.changeset/provider-requires-content-bound-prompt.md b/.changeset/provider-requires-content-bound-prompt.md
new file mode 100644
index 00000000..4ae3c604
--- /dev/null
+++ b/.changeset/provider-requires-content-bound-prompt.md
@@ -0,0 +1,19 @@
+---
+"@tangle-network/agent-provider-tangle": patch
+"@tangle-network/agent-provider-cli-bridge": patch
+---
+
+Require an `@tangle-network/agent-interface` that bounds a turn prompt as content.
+
+Both packages validate a turn with `AgentTurnInputSchema`, so the agent-interface copy each one
+resolves decides what a turn may contain — not the copy the consumer installed at its own top level.
+agent-interface 2.7.0 moved every `prompt` field off the 16 KiB metadata bound onto the 1 MiB content
+bound, and 2.8.0 made the contract bound constants public. The Tangle provider still declared `^2.6.1`
+and the CLI bridge `^2.4.0`, so a consumer whose lockfile already held an older entry kept validating
+turns against the metadata bound on a stack whose manifests said the bug was fixed.
+
+The Tangle provider now requires `^2.8.0`, because it also imports the contract bounds that became
+public there. The CLI bridge requires `^2.7.0`, the release that changed the bound it validates with.
+`resolved-interface-floor.test.ts` fails when the Tangle provider resolves an agent-interface below
+its declared floor, when the declared floor is below the release its validation needs, or when the
+resolved copy refuses a prompt larger than the metadata bound.
diff --git a/packages/agent-provider-cli-bridge/package.json b/packages/agent-provider-cli-bridge/package.json
index d093c27c..554e3d1c 100644
--- a/packages/agent-provider-cli-bridge/package.json
+++ b/packages/agent-provider-cli-bridge/package.json
@@ -80,7 +80,7 @@
     "test:integration": "test -n \"$CLI_BRIDGE_INTEGRATION_ROOT\" || { echo 'CLI_BRIDGE_INTEGRATION_ROOT is required; see README' >&2; exit 1; }; pnpm run build && vitest run tests/cli-bridge.integration.test.ts"
   },
   "dependencies": {
-    "@tangle-network/agent-interface": "^2.4.0",
+    "@tangle-network/agent-interface": "^2.7.0",
     "undici": "catalog:"
   },
   "devDependencies": {
diff --git a/packages/agent-provider-tangle/package.json b/packages/agent-provider-tangle/package.json
index 85ff1b64..26710155 100644
--- a/packages/agent-provider-tangle/package.json
+++ b/packages/agent-provider-tangle/package.json
@@ -112,7 +112,7 @@
     "test": "vitest run src"
   },
   "dependencies": {
-    "@tangle-network/agent-interface": "^2.6.1"
+    "@tangle-network/agent-interface": "^2.8.0"
   },
   "peerDependencies": {
     "@tangle-network/sandbox": ">=0.39.0 <1.0.0"
diff --git a/packages/agent-provider-tangle/src/resolved-interface-floor.test.ts b/packages/agent-provider-tangle/src/resolved-interface-floor.test.ts
new file mode 100644
index 00000000..e6adde7e
--- /dev/null
+++ b/packages/agent-provider-tangle/src/resolved-interface-floor.test.ts
@@ -0,0 +1,191 @@
+import { existsSync, readFileSync } from "node:fs";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+// A NAMESPACE import on purpose. A named import of a constant that an older resolution does not
+// export fails at module link time with a SyntaxError that names the missing binding and nothing
+// else — no package, no version, no reason. This file exists to diagnose exactly that resolution,
+// so it has to survive one long enough to say what is wrong with it.
+import * as agentInterface from "@tangle-network/agent-interface";
+import { describe, expect, it } from "vitest";
+import { promptFromTurnInput } from "./tangle-prompt.js";
+
+/**
+ * This package is the code that VALIDATES a turn, so the agent-interface copy it resolves decides
+ * what a turn may contain — not the copy the consumer installed at its own top level.
+ *
+ * agent-interface 2.7.0 (agent-sdk#314) moved every `prompt` field off the 16 KiB metadata bound
+ * (`CONTRACT_MAX_STRING_LENGTH`) onto the 1 MiB content bound, and 2.8.0 (#315) made the contract
+ * bound constants public. This package kept declaring `^2.6.1`, which admits both older versions.
+ *
+ * Measured 2026-09-11: a consumer whose lockfile already held 2.6.1 for this package, and which
+ * then raised its own top-level agent-interface to 2.8.0, ended up with TWO copies — agent-runtime
+ * on 2.8.0, this provider on 2.6.1. Because this provider is what validates, children kept dying on
+ * the 16 KiB bound with a ZodError at `path: ["prompt"]` on a stack whose package.json said the bug
+ * was fixed: 14 of 34 children of one run and 8 of 52 of another, every one at iterations 0,
+ * surfaced as "retained provider execution requires reconciliation before replacement".
+ *
+ * `producer-consumer-bounds.test.ts` cannot see this. It reads the shipped Sandbox dist and
+ * compares it against contract constants it imports, and the workspace pins
+ * `overrides["@tangle-network/agent-interface"]: workspace:*`, so inside this repo it always links
+ * the workspace copy. This file checks the other half: which agent-interface this package would
+ * resolve, and what that resolution actually accepts.
+ */
+
+/**
+ * The agent-interface version this package's own validation needs.
+ *
+ * 2.7.0 is where a prompt stopped being metadata. 2.8.0 is where CONTRACT_MAX_ARRAY_LENGTH,
+ * CONTRACT_MAX_IDENTIFIER_LENGTH and CONTRACT_MAX_STRING_LENGTH became public, which is what lets
+ * this package assert its own bounds at all. Both are load-bearing here, so the floor is the later
+ * one. A range that admits less than this is the defect, and it is invisible in a workspace that
+ * overrides the resolution, so it is asserted rather than left to review.
+ */
+const REQUIRED_INTERFACE_FLOOR = "2.8.0";
+
+/** The metadata bound's value, written out because a resolution old enough to fail this file is
+ *  also too old to export the constant. One case below asserts the two agree. */
+const METADATA_BOUND = 16_384;
+
+interface Manifest {
+  readonly version?: string;
+  readonly dependencies?: Record<string, string>;
+}
+
+function readManifest(path: string): Manifest {
+  return JSON.parse(readFileSync(path, "utf8")) as Manifest;
+}
+
+const packageRoot = join(dirname(fileURLToPath(import.meta.url)), "..");
+const selfManifest = readManifest(join(packageRoot, "package.json"));
+
+/**
+ * The agent-interface copy this package's imports bind to.
+ *
+ * `require.resolve("@tangle-network/agent-interface/package.json")` cannot be used: that package's
+ * `exports` map declares no "./package.json" subpath and no `require` condition, so Node refuses
+ * both the subpath and the entry point from CommonJS. Walk the `node_modules` chain the way Node
+ * locates the package directory for a bare specifier, which finds the copy that would be loaded.
+ */
+function resolvedInterfaceVersion(): string {
+  let directory = packageRoot;
+  for (;;) {
+    const candidate = join(
+      directory,
+      "node_modules",
+      "@tangle-network",
+      "agent-interface",
+      "package.json",
+    );
+    if (existsSync(candidate)) {
+      const manifest = readManifest(candidate);
+      if (typeof manifest.version !== "string") {
+        throw new Error(`${candidate} declares no version`);
+      }
+      return manifest.version;
+    }
+    const parent = dirname(directory);
+    if (parent === directory) break;
+    directory = parent;
+  }
+  throw new Error(
+    "no @tangle-network/agent-interface is installed for this package. Find what changed in its packaging or install; do not delete this check.",
+  );
+}
+
+/** `^X.Y.Z` only. Any other shape is refused rather than guessed at, so a range this check cannot
+ *  reason about fails here instead of passing silently. */
+function declaredFloor(range: string | undefined): string {
+  const match = /^\^(\d+\.\d+\.\d+)$/.exec(range ?? "");
+  if (match === null) {
+    throw new Error(
+      `agent-provider-tangle declares ${JSON.stringify(range)} for @tangle-network/agent-interface. This check only reasons about a caret range; teach it the new shape rather than removing it.`,
+    );
+  }
+  return match[1];
+}
+
+function compareVersions(left: string, right: string): number {
+  const leftParts = left.split(".").map(Number);
+  const rightParts = right.split(".").map(Number);
+  for (let index = 0; index < 3; index += 1) {
+    if (leftParts[index] !== rightParts[index]) return leftParts[index] - rightParts[index];
+  }
+  return 0;
+}
+
+describe("the agent-interface resolution this provider validates with", () => {
+  // Behaviour first: the declared range can be right while the code behind it is not.
+  it("accepts a turn prompt larger than the metadata bound", () => {
+    const prompt = "x".repeat(METADATA_BOUND + 1);
+    expect(
+      () => promptFromTurnInput({ prompt }),
+      `the resolved @tangle-network/agent-interface (${resolvedInterfaceVersion()}) still holds a turn prompt to the ${METADATA_BOUND}-character metadata bound. Every oversized turn this provider validates dies at iterations 0 (agent-sdk#314).`,
+    ).not.toThrow();
+    expect(promptFromTurnInput({ prompt })).toBe(prompt);
+  });
+
+  it("does not refuse an interactive prompt for its length", () => {
+    // The digest and the session coordinates are deliberately unmatched, so this command is
+    // invalid. The assertion is only that `prompt` is not among the reasons: a length issue here is
+    // the metadata bound reaching the interactive site this provider parses in `sendPrompt`.
+    const result = agentInterface.AgentInteractiveSessionPromptCommandSchema.safeParse({
+      operationId: "interface-floor-probe",
+      ref: {
+        provider: "tangle-sandbox",
+        environmentId: "sandbox-1",
+        sessionId: "session-1",
+        executionId: "execution-1",
+        requestDigest: `sha256:${"a".repeat(64)}`,
+      },
+      control: {
+        refDigest: `sha256:${"b".repeat(64)}`,
+        incarnationId: "incarnation-1",
+        claimedAtMs: 1,
+      },
+      prompt: "x".repeat(METADATA_BOUND + 1),
+      requestDigest: `sha256:${"c".repeat(64)}`,
+    });
+    const promptIssues = result.success
+      ? []
+      : result.error.issues.filter((issue) => issue.path[0] === "prompt");
+    expect(
+      promptIssues,
+      `the resolved @tangle-network/agent-interface (${resolvedInterfaceVersion()}) refuses an interactive prompt for its size, which is the metadata bound reaching the site this provider parses in sendPrompt (agent-sdk#314).`,
+    ).toEqual([]);
+  });
+
+  it("exports the contract bounds this package validates its own limits against", () => {
+    // producer-consumer-bounds.test.ts imports these by name. On a resolution older than 2.8.0 that
+    // file does not fail, it fails to LOAD, which is how the seam it guards stops being checked.
+    expect(
+      agentInterface.CONTRACT_MAX_STRING_LENGTH,
+      `the resolved @tangle-network/agent-interface (${resolvedInterfaceVersion()}) does not export CONTRACT_MAX_STRING_LENGTH, which became public in ${REQUIRED_INTERFACE_FLOOR} (agent-sdk#315).`,
+    ).toBe(METADATA_BOUND);
+    expect(agentInterface.CONTRACT_MAX_IDENTIFIER_LENGTH).toBeTypeOf("number");
+    expect(agentInterface.CONTRACT_MAX_ARRAY_LENGTH).toBeTypeOf("number");
+    expect(agentInterface.CONTRACT_MAX_JSON_BYTES).toBeTypeOf("number");
+  });
+
+  it("resolves an agent-interface at or above the range this package declares", () => {
+    const floor = declaredFloor(selfManifest.dependencies?.["@tangle-network/agent-interface"]);
+    const resolved = resolvedInterfaceVersion();
+    expect(
+      compareVersions(resolved, floor),
+      `this package resolves @tangle-network/agent-interface ${resolved}, below its declared floor ${floor}. A consumer holding an older lockfile entry gets exactly this split: its runtime on the new contract, its validator on the old one.`,
+    ).toBeGreaterThanOrEqual(0);
+    // A caret range also has to stay inside the major it was written against.
+    expect(Number(resolved.split(".")[0])).toBe(Number(floor.split(".")[0]));
+  });
+
+  it("declares a floor at least as high as the contract change its validation needs", () => {
+    // Without this the behaviour cases above can pass for the wrong reason: inside this workspace
+    // the resolution is overridden to the workspace copy, so a range lowered back to ^2.4.0 would
+    // still resolve something new enough to accept a large prompt, and only a consumer would find
+    // out.
+    const floor = declaredFloor(selfManifest.dependencies?.["@tangle-network/agent-interface"]);
+    expect(
+      compareVersions(floor, REQUIRED_INTERFACE_FLOOR),
+      `agent-provider-tangle declares ^${floor} for @tangle-network/agent-interface but its validation needs ${REQUIRED_INTERFACE_FLOOR}: the content-bound prompt (2.7.0) and the public contract bounds (2.8.0). Raise the range, or move this floor and say what changed.`,
+    ).toBeGreaterThanOrEqual(0);
+  });
+});