diff --git a/src/api/routes.ts b/src/api/routes.ts
index aa8ceff4ab..7b1eeb78d1 100644
--- a/src/api/routes.ts
+++ b/src/api/routes.ts
@@ -23,6 +23,7 @@ import {
 } from "../auth/security";
 import { normalizeGittBountySnapshot } from "../bounties/ingest";
 import { DEFAULT_COMMAND_AUTHORIZATION_POLICY, normalizeCommandAuthorizationPolicy } from "../settings/command-authorization";
+import { SCENARIO_MAX_BRANCH_REF_CHARS, SCENARIO_MAX_LINKED_ISSUE_NUMBERS, SCENARIO_MAX_REPO_FULL_NAME_CHARS } from "../scenarios/input-model";
 import {
   countOpenIssues,
   countOpenPullRequests,
@@ -410,10 +411,10 @@ const branchEligibilitySchema = z
 const localBranchAnalysisSchema = z
   .object({
     login: z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS),
-    repoFullName: z.string().min(3).max(MAX_LOCAL_BRANCH_REF_CHARS),
-    baseRef: z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS).optional(),
-    headRef: z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS).optional(),
-    branchName: z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS).optional(),
+    repoFullName: z.string().min(3).max(SCENARIO_MAX_REPO_FULL_NAME_CHARS),
+    baseRef: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
+    headRef: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
+    branchName: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
     baseSha: z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS).optional(),
     headSha: z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS).optional(),
     mergeBaseSha: z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS).optional(),
@@ -421,7 +422,7 @@ const localBranchAnalysisSchema = z
     commitMessages: z.array(z.string().max(MAX_LOCAL_BRANCH_TEXT_CHARS)).max(30).optional(),
     changedFiles: z.array(localBranchChangedFileSchema).max(500).optional(),
     validation: z.array(localBranchValidationSchema).max(50).optional(),
-    linkedIssues: z.array(z.number().int().positive()).optional(),
+    linkedIssues: z.array(z.number().int().positive()).max(SCENARIO_MAX_LINKED_ISSUE_NUMBERS).optional(),
     labels: z.array(z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS)).max(50).optional(),
     title: z.string().min(1).max(MAX_LOCAL_BRANCH_REF_CHARS).optional(),
     body: z.string().max(MAX_LOCAL_BRANCH_TEXT_CHARS).optional(),
diff --git a/src/mcp/server.ts b/src/mcp/server.ts
index 3535179f26..65cb99cfef 100644
--- a/src/mcp/server.ts
+++ b/src/mcp/server.ts
@@ -79,6 +79,7 @@ import { buildLocalBranchAnalysis, findCurrentBranchPullRequest } from "../signa
 import { loadRepoFocusManifest } from "../signals/focus-manifest-loader";
 import { buildRepoDataQuality } from "../signals/data-quality";
 import { PREFLIGHT_LIMITS } from "../signals/preflight-limits";
+import { SCENARIO_MAX_BRANCH_REF_CHARS, SCENARIO_MAX_LINKED_ISSUE_NUMBERS, SCENARIO_MAX_REPO_FULL_NAME_CHARS } from "../scenarios/input-model";
 import { loadUpstreamStatus } from "../upstream/ruleset";
 
 type AppContext = Context<{ Bindings: Env }>;
@@ -162,11 +163,11 @@ const branchEligibilityShape = {
 };
 
 const localBranchAnalysisShape = {
-  login: z.string().min(1),
-  repoFullName: z.string().min(3),
-  baseRef: z.string().min(1).optional(),
-  headRef: z.string().min(1).optional(),
-  branchName: z.string().min(1).optional(),
+  login: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS),
+  repoFullName: z.string().min(3).max(SCENARIO_MAX_REPO_FULL_NAME_CHARS),
+  baseRef: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
+  headRef: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
+  branchName: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
   baseSha: z.string().min(1).optional(),
   headSha: z.string().min(1).optional(),
   mergeBaseSha: z.string().min(1).optional(),
@@ -201,7 +202,7 @@ const localBranchAnalysisShape = {
     )
     .max(50)
     .optional(),
-  linkedIssues: z.array(z.number().int().positive()).optional(),
+  linkedIssues: z.array(z.number().int().positive()).max(SCENARIO_MAX_LINKED_ISSUE_NUMBERS).optional(),
   labels: z.array(z.string()).optional(),
   title: z.string().min(1).optional(),
   body: z.string().optional(),
diff --git a/src/scenarios/input-model.ts b/src/scenarios/input-model.ts
index 109c66dab4..f7a08d9973 100644
--- a/src/scenarios/input-model.ts
+++ b/src/scenarios/input-model.ts
@@ -2,6 +2,10 @@ import { z } from "zod";
 import { sanitizePublicComment } from "../github/commands";
 
 export const SCENARIO_INPUT_VERSION = 1 as const;
+export const SCENARIO_MAX_REPO_FULL_NAME_CHARS = 200;
+export const SCENARIO_MAX_BRANCH_REF_CHARS = 200;
+export const SCENARIO_MAX_LINKED_ISSUE_NUMBERS = 50;
+export const SCENARIO_MAX_SIGNAL_DETAIL_CHARS = 2000;
 
 export const scenarioInputKinds = ["fact", "assumption", "estimate", "unavailable"] as const;
 export type ScenarioInputKind = (typeof scenarioInputKinds)[number];
@@ -36,7 +40,7 @@ const scenarioSignalEntrySchema = z
     id: z.string().min(1).max(120),
     kind: z.enum(scenarioInputKinds),
     label: z.string().min(1).max(200),
-    detail: z.string().min(1).max(2000),
+    detail: z.string().min(1).max(SCENARIO_MAX_SIGNAL_DETAIL_CHARS),
     source: z.enum(scenarioSignalSources),
   })
   .strict();
@@ -45,7 +49,7 @@ export type ScenarioSignalEntry = z.infer<typeof scenarioSignalEntrySchema>;
 
 const scenarioRepoConfigSchema = z
   .object({
-    repoFullName: z.string().min(3).max(200),
+    repoFullName: z.string().min(3).max(SCENARIO_MAX_REPO_FULL_NAME_CHARS),
     registered: z.boolean().optional(),
     maintainerLane: z.boolean().optional(),
   })
@@ -56,7 +60,7 @@ export type ScenarioRepoConfig = z.infer<typeof scenarioRepoConfigSchema>;
 const scenarioIssueStateSchema = z
   .object({
     openIssueCount: z.number().int().min(0).optional(),
-    linkedIssueNumbers: z.array(z.number().int().positive()).max(50).optional(),
+    linkedIssueNumbers: z.array(z.number().int().positive()).max(SCENARIO_MAX_LINKED_ISSUE_NUMBERS).optional(),
   })
   .strict();
 
@@ -75,9 +79,9 @@ export type ScenarioPullRequestState = z.infer<typeof scenarioPullRequestStateSc
 
 const scenarioBranchStateSchema = z
   .object({
-    branchName: z.string().min(1).max(200).optional(),
-    baseRef: z.string().min(1).max(200).optional(),
-    headRef: z.string().min(1).max(200).optional(),
+    branchName: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
+    baseRef: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
+    headRef: z.string().min(1).max(SCENARIO_MAX_BRANCH_REF_CHARS).optional(),
     pendingCommitCount: z.number().int().min(0).optional(),
     changedFileCount: z.number().int().min(0).optional(),
     eligibilityStatus: z.enum(["eligible", "ineligible", "unknown"]).optional(),
@@ -219,40 +223,49 @@ export function scenarioInputFromLocalBranchMetadata(args: {
   scenarioNotes?: string[];
   eligibilityStatus?: "eligible" | "ineligible" | "unknown";
 }): AgentScenarioInput {
+  const login = trimScenarioText(args.login, SCENARIO_MAX_BRANCH_REF_CHARS);
+  const repoFullName = trimScenarioText(args.repoFullName, SCENARIO_MAX_REPO_FULL_NAME_CHARS);
+  const branchName = optionalScenarioText(args.branchName, SCENARIO_MAX_BRANCH_REF_CHARS);
+  const baseRef = optionalScenarioText(args.baseRef, SCENARIO_MAX_BRANCH_REF_CHARS);
+  const linkedIssues = args.linkedIssues?.slice(0, SCENARIO_MAX_LINKED_ISSUE_NUMBERS);
+  const scenarioNotes = args.scenarioNotes
+    ?.map((note) => trimScenarioText(note, SCENARIO_MAX_SIGNAL_DETAIL_CHARS))
+    .filter((note) => note.length > 0);
+
   const facts: ScenarioSignalEntry[] = [
     createScenarioSignalEntry({
       id: "actor",
       kind: "fact",
       label: "Contributor",
-      detail: `Planning scenario for ${args.login}.`,
+      detail: `Planning scenario for ${login}.`,
       source: "github_observed",
     }),
     createScenarioSignalEntry({
       id: "repo",
       kind: "fact",
       label: "Repository",
-      detail: `Repo context is ${args.repoFullName}.`,
+      detail: `Repo context is ${repoFullName}.`,
       source: "local_metadata",
     }),
   ];
-  if (args.branchName) {
+  if (branchName) {
     facts.push(
       createScenarioSignalEntry({
         id: "branch",
         kind: "fact",
         label: "Branch",
-        detail: `Active branch ${args.branchName}${args.baseRef ? ` against ${args.baseRef}` : ""}.`,
+        detail: `Active branch ${branchName}${baseRef ? ` against ${baseRef}` : ""}.`,
         source: "local_metadata",
       }),
     );
   }
   const assumptions =
-    args.scenarioNotes?.map((note, index) =>
+    scenarioNotes?.map((note, index) =>
       createScenarioSignalEntry({
         id: `assumption_${index + 1}`,
         kind: "assumption",
         label: "Caller assumption",
-        detail: note.trim(),
+        detail: note,
         source: "user_supplied",
       }),
     ) ?? [];
@@ -268,12 +281,17 @@ export function scenarioInputFromLocalBranchMetadata(args: {
       }),
     );
   }
-  const branchState = compactBranchState(args);
+  const branchState = compactBranchState({
+    ...(branchName ? { branchName } : {}),
+    ...(baseRef ? { baseRef } : {}),
+    ...(args.changedFileCount !== undefined ? { changedFileCount: args.changedFileCount } : {}),
+    ...(args.eligibilityStatus ? { eligibilityStatus: args.eligibilityStatus } : {}),
+  });
   return buildScenarioInput({
     scenarioType: args.scenarioType,
-    repoFullName: args.repoFullName,
+    repoFullName,
     ...(branchState ? { branchState } : {}),
-    ...(args.linkedIssues?.length ? { issueState: { linkedIssueNumbers: args.linkedIssues } } : {}),
+    ...(linkedIssues?.length ? { issueState: { linkedIssueNumbers: linkedIssues } } : {}),
     facts,
     assumptions,
     unavailableSignals,
@@ -339,6 +357,16 @@ function validateBucketKinds(
   }
 }
 
+function trimScenarioText(value: string, maxLength: number): string {
+  return value.trim().slice(0, maxLength);
+}
+
+function optionalScenarioText(value: string | undefined, maxLength: number): string | undefined {
+  if (!value) return undefined;
+  const trimmed = trimScenarioText(value, maxLength);
+  return trimmed.length > 0 ? trimmed : undefined;
+}
+
 function sortEntries(entries: ScenarioSignalEntry[]): ScenarioSignalEntry[] {
   return [...entries].sort((left, right) => left.id.localeCompare(right.id));
 }
diff --git a/test/unit/local-branch.test.ts b/test/unit/local-branch.test.ts
index 31dfa9b86a..01eeb1171c 100644
--- a/test/unit/local-branch.test.ts
+++ b/test/unit/local-branch.test.ts
@@ -4,6 +4,7 @@ import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { pathToFileURL } from "node:url";
 import { afterEach, describe, expect, it } from "vitest";
+import { SCENARIO_MAX_BRANCH_REF_CHARS, SCENARIO_MAX_LINKED_ISSUE_NUMBERS } from "../../src/scenarios/input-model";
 import { buildLocalBranchAnalysis, findCurrentBranchPullRequest } from "../../src/signals/local-branch";
 import { MAX_LOCAL_SCORER_WARNING_CHARS, MAX_LOCAL_SCORER_WARNING_COUNT } from "../../src/signals/local-scorer-diagnostics";
 import type { ContributorOutcomeHistory, ContributorProfile, ContributorScoringProfile, IssueQualityReport } from "../../src/signals/engine";
@@ -1593,6 +1594,30 @@ describe("local MCP git metadata collection", () => {
     expect(analysis.scenarioSummary.dataClassification.facts).toContain("Branch");
   });
 
+  it("does not throw while summarizing oversized local branch metadata", () => {
+    const analysis = buildLocalBranchAnalysis({
+      input: {
+        login: "oktofeesh1",
+        repoFullName: repo.fullName,
+        branchName: "b".repeat(SCENARIO_MAX_BRANCH_REF_CHARS + 1),
+        baseRef: "m".repeat(SCENARIO_MAX_BRANCH_REF_CHARS + 1),
+        linkedIssues: Array.from({ length: SCENARIO_MAX_LINKED_ISSUE_NUMBERS + 1 }, (_, index) => index + 1),
+        changedFiles: [{ path: "src/util.ts", additions: 20, deletions: 1, status: "modified" }],
+        localScorer: { mode: "external_command", sourceTokenScore: 35, totalTokenScore: 55, sourceLines: 30 },
+      },
+      repo,
+      issues: [],
+      pullRequests: [],
+      profile,
+      outcomeHistory,
+      scoringSnapshot,
+      scoringProfile,
+    });
+
+    expect(analysis.scenarioSummary.dataClassification.facts).toContain("Branch");
+    expect(analysis.branchName).toHaveLength(SCENARIO_MAX_BRANCH_REF_CHARS + 1);
+  });
+
   it("populates scenarioSummary.eligibilityNotes from the derived eligibility plan", () => {
     const analysis = buildLocalBranchAnalysis({
       input: {
diff --git a/test/unit/scenario-input-model.test.ts b/test/unit/scenario-input-model.test.ts
index 1575a698b8..28e17d8161 100644
--- a/test/unit/scenario-input-model.test.ts
+++ b/test/unit/scenario-input-model.test.ts
@@ -1,5 +1,9 @@
 import { describe, expect, it } from "vitest";
 import {
+  SCENARIO_MAX_BRANCH_REF_CHARS,
+  SCENARIO_MAX_LINKED_ISSUE_NUMBERS,
+  SCENARIO_MAX_REPO_FULL_NAME_CHARS,
+  SCENARIO_MAX_SIGNAL_DETAIL_CHARS,
   assertScenarioLocalBranchInputSafe,
   buildScenarioInput,
   createScenarioSignalEntry,
@@ -264,6 +268,24 @@ describe("source-upload safety", () => {
     expect(input.unavailableSignals[0]?.kind).toBe("unavailable");
     expect(JSON.stringify(input)).not.toMatch(/fileContent|sourceContent|upload/i);
   });
+
+  it("bounds local branch metadata before scenario validation", () => {
+    const input = scenarioInputFromLocalBranchMetadata({
+      scenarioType: "branch_preflight",
+      login: "miner",
+      repoFullName: `octo/${"r".repeat(260)}`,
+      branchName: "b".repeat(260),
+      baseRef: "m".repeat(260),
+      linkedIssues: Array.from({ length: 75 }, (_, index) => index + 1),
+      scenarioNotes: ["n".repeat(SCENARIO_MAX_SIGNAL_DETAIL_CHARS + 100)],
+    });
+
+    expect(input.repo.repoFullName).toHaveLength(SCENARIO_MAX_REPO_FULL_NAME_CHARS);
+    expect(input.branchState?.branchName).toHaveLength(SCENARIO_MAX_BRANCH_REF_CHARS);
+    expect(input.branchState?.baseRef).toHaveLength(SCENARIO_MAX_BRANCH_REF_CHARS);
+    expect(input.issueState?.linkedIssueNumbers).toHaveLength(SCENARIO_MAX_LINKED_ISSUE_NUMBERS);
+    expect(input.assumptions[0]?.detail).toHaveLength(SCENARIO_MAX_SIGNAL_DETAIL_CHARS);
+  });
 });
 
 describe("invariants", () => {