diff --git a/src/shared/load-opencode-plugins.ts b/src/shared/load-opencode-plugins.ts
index a6beffdcf..1d8664aa7 100644
--- a/src/shared/load-opencode-plugins.ts
+++ b/src/shared/load-opencode-plugins.ts
@@ -51,12 +51,12 @@ export function loadOpencodePlugins(directory: string): string[] {
       const result = parseJsoncSafe<OpencodeConfig>(content)
       const plugins = result.data?.plugin ?? []
 
-      for (const rawPlugin of plugins) {
-        const plugin = typeof rawPlugin === "string" ? rawPlugin : Array.isArray(rawPlugin) ? rawPlugin[0] : null
-        if (typeof plugin !== "string") continue
-        if (seenPluginEntries.has(plugin)) continue
-        seenPluginEntries.add(plugin)
-        pluginEntries.push(plugin)
+      for (const plugin of plugins) {
+        const entry = typeof plugin === "string" ? plugin : Array.isArray(plugin) ? plugin[0] : null
+        if (typeof entry !== "string") continue
+        if (seenPluginEntries.has(entry)) continue
+        seenPluginEntries.add(entry)
+        pluginEntries.push(entry)
       }
     } catch {
       continue
diff --git a/src/shared/model-capabilities/runtime-model-readers.test.ts b/src/shared/model-capabilities/runtime-model-readers.test.ts
new file mode 100644
index 000000000..2433d9a45
--- /dev/null
+++ b/src/shared/model-capabilities/runtime-model-readers.test.ts
@@ -0,0 +1,111 @@
+import { describe, expect, it } from "bun:test"
+import { readRuntimeModelModalities } from "./runtime-model-readers"
+
+describe("readRuntimeModelModalities", () => {
+	describe("object-shaped modalities (OpenCode schema)", () => {
+		it("#given modalities with input/output string arrays #when reading runtime model #then returns normalized modalities", () => {
+			const runtimeModel = {
+				id: "test-model",
+				modalities: {
+					input: ["text", "image", "pdf"],
+					output: ["text"],
+				},
+			}
+
+			const result = readRuntimeModelModalities(runtimeModel as Record<string, unknown>)
+
+			expect(result).toBeDefined()
+			expect(result?.input).toEqual(["text", "image", "pdf"])
+			expect(result?.output).toEqual(["text"])
+		})
+
+		it("#given modalities with mixed-case strings #when reading runtime model #then lowercases all entries", () => {
+			const runtimeModel = {
+				id: "test-model",
+				modalities: {
+					input: ["Text", "IMAGE", "Pdf"],
+					output: ["TEXT"],
+				},
+			}
+
+			const result = readRuntimeModelModalities(runtimeModel as Record<string, unknown>)
+
+			expect(result?.input).toEqual(["text", "image", "pdf"])
+			expect(result?.output).toEqual(["text"])
+		})
+
+		it("#given modalities nested in capabilities #when reading runtime model #then finds and normalizes them", () => {
+			const runtimeModel = {
+				id: "test-model",
+				capabilities: {
+					modalities: {
+						input: ["text", "audio"],
+						output: ["text"],
+					},
+				},
+			}
+
+			const result = readRuntimeModelModalities(runtimeModel as Record<string, unknown>)
+
+			expect(result).toBeDefined()
+			expect(result?.input).toEqual(["text", "audio"])
+			expect(result?.output).toEqual(["text"])
+		})
+	})
+
+	describe("flat string array modalities", () => {
+		it("#given modalities as boolean map at top level #when reading runtime model #then returns undefined (not supported at this level)", () => {
+			const runtimeModel = {
+				id: "test-model",
+				modalities: {
+					text: true,
+					image: true,
+					audio: false,
+				},
+			}
+
+			const result = readRuntimeModelModalities(runtimeModel as Record<string, unknown>)
+
+			// Boolean maps are only recognized inside input/output keys, not at the modalities root
+			expect(result).toBeUndefined()
+		})
+	})
+
+	describe("no crash on unexpected shapes", () => {
+		it("#given modalities is undefined #when reading runtime model #then returns undefined", () => {
+			const runtimeModel = { id: "test-model" }
+
+			const result = readRuntimeModelModalities(runtimeModel as Record<string, unknown>)
+
+			expect(result).toBeUndefined()
+		})
+
+		it("#given modalities contains nested arrays #when reading runtime model #then does not throw", () => {
+			const runtimeModel = {
+				id: "test-model",
+				modalities: {
+					input: [["text", "image"], ["pdf"]],
+					output: [["text"]],
+				},
+			}
+
+			expect(() => {
+				readRuntimeModelModalities(runtimeModel as Record<string, unknown>)
+			}).not.toThrow()
+		})
+
+		it("#given modalities values are non-string non-array #when reading runtime model #then does not throw", () => {
+			const runtimeModel = {
+				id: "test-model",
+				modalities: {
+					input: 42,
+					output: null,
+				},
+			}
+
+			expect(() => {
+				readRuntimeModelModalities(runtimeModel as Record<string, unknown>)
+			}).not.toThrow()
+		})
+	})
+})
diff --git a/src/shared/model-capabilities/runtime-model-readers.ts b/src/shared/model-capabilities/runtime-model-readers.ts
index a7b740f32..55b54e077 100644
--- a/src/shared/model-capabilities/runtime-model-readers.ts
+++ b/src/shared/model-capabilities/runtime-model-readers.ts
@@ -22,7 +22,7 @@ function readStringArray(value: unknown): string[] | undefined {
 function normalizeVariantKeys(value: unknown): string[] | undefined {
 	const arrayVariants = readStringArray(value)
 	if (arrayVariants) {
-		return arrayVariants.map((variant) => variant.toLowerCase())
+		return arrayVariants.filter((v): v is string => typeof v === "string").map((variant) => variant.toLowerCase())
 	}
 
 	if (!isRecord(value)) {
@@ -36,13 +36,24 @@ function normalizeVariantKeys(value: unknown): string[] | undefined {
 function readModalityKeys(value: unknown): string[] | undefined {
 	const stringArray = readStringArray(value)
 	if (stringArray) {
-		return stringArray.map((entry) => entry.toLowerCase())
+		return stringArray.filter((entry): entry is string => typeof entry === "string").map((entry) => entry.toLowerCase())
 	}
 
 	if (!isRecord(value)) {
 		return undefined
 	}
 
+	// Handle OpenCode's object-shaped modalities: { input: string[], output: string[] }
+	// When the full modalities object reaches here (e.g. via the normalizeModalities
+	// fallback path), flatten nested string arrays before applying toLowerCase.
+	const fromNested = Object.values(value)
+		.filter((v): v is string[] => Array.isArray(v))
+		.flat()
+		.filter((item): item is string => typeof item === "string")
+	if (fromNested.length > 0) {
+		return fromNested.map((entry) => entry.toLowerCase())
+	}
+
 	const enabled = Object.entries(value)
 		.filter(([, supported]) => supported === true)
 		.map(([modality]) => modality.toLowerCase())