feat(chat): paste-to-attach images/PDFs with model capability check

Add multimodal image/PDF input to the chat box via clipboard paste, gated by a
graceful per-model capability check.

UX: a pasted image/PDF inserts an inline token (【image:…】 / 【pdf:…】) into the
draft, so attachments have ORDER relative to typed text and can be referenced
positionally. The token is the only handle — deleting it (atomic Backspace/
Delete, or selection overlap) detaches the file; an input-reconciliation safety
net detaches any attachment whose token is no longer intact. No preview strip.

Capability check: resolveModelCapabilities reads models.dev modalities.input
(new GET /models/capabilities, mirrors /context-limit). The input blocks Send
(no tokens spent) only on a definitive 'no'; unknown capability (catalog offline
/ unmapped provider) stays permissive. Attachments require a fresh turn — Send is
blocked while generating and /chat rejects content mid-turn (409).

Attachments are EPHEMERAL: forwarded to the model for the turn via ordered AI SDK
ImagePart/FilePart content, but never persisted (history keeps the text with
[image]/[pdf] markers). Text-only turns serialize byte-identically to before.

Limits (Anthropic-aligned, enforced at paste + re-validated server-side):
PNG/JPEG/WebP/GIF/PDF; image ≤5MB, PDF ≤32MB, ≤20 attachments, ≤32MB total.

core: UserContentPart types, models/attachments validator, capability resolver,
agent.run+toModelMessages thread ordered content. api: /chat content validation +
passthrough. frontend: attachment-tokens helper, ChatInput paste/token/gating,
per-tab staged attachments, App.svelte capability fetch. +44 tests.

1 files changed, 11 insertions, 0 deletions

diff --git a/packages/api/src/agent-manager.ts b/packages/api/src/agent-manager.ts
index 2532efa..3b12a80 100644
--- a/packages/api/src/agent-manager.ts
+++ b/packages/api/src/agent-manager.ts
@@ -65,6 +65,7 @@ import {
 	toAvailableUserAgents,
 	type UsageData,
 	type UsageStats,
+	type UserContentPart,
 	validateConfig,
 } from "@dispatch/core";
 import type { PermissionManager } from "./permission-manager.js";
@@ -1536,6 +1537,13 @@ export class AgentManager {
 			workingDirectory?: string;
 			queueId?: string;
 			/**
+			 * Ephemeral ordered multimodal content (image/pdf attachments) for a
+			 * FRESH human turn. Forwarded to `processMessage` → `agent.run` only
+			 * when the tab is idle (a started turn); never carried into the queue
+			 * path (attachments require a fresh turn — the caller guards that).
+			 */
+			content?: UserContentPart[];
+			/**
 			 * Who is sending this message. `"human"` (default) is unrestricted
 			 * and REFILLS the target's agent-to-agent auto-wake budget. `"agent"`
 			 * (from the `send_to_tab` tool) is governed by that budget: an
@@ -1606,6 +1614,7 @@ export class AgentManager {
 			opts.reasoningEffort,
 			opts.workingDirectory,
 			agentModels,
+			opts.content,
 		).catch((err) => {
 			console.error(`[dispatch] deliverMessage processMessage error for tab ${tabId}:`, err);
 		});
@@ -1620,6 +1629,7 @@ export class AgentManager {
 		reasoningEffort?: ReasoningEffort,
 		workingDirectory?: string,
 		agentModels?: AgentModelEntry[],
+		content?: UserContentPart[],
 	): Promise<void> {
 		const tabAgent = this._getOrCreateTabAgent(tabId);
 
@@ -1731,6 +1741,7 @@ export class AgentManager {
 				for await (const event of agent.run(message, {
 					...(effortForEntry ? { reasoningEffort: effortForEntry } : {}),
 					abortSignal: tabAgent.abortController?.signal,
+					...(content ? { content } : {}),
 				})) {
 					// Stop processing if the tab was aborted (closed/stopped).
 					// stopTab() already injected a `cancelled` system chunk into