feat(tabs): tab-to-tab agent communication via short handles

Add send_to_tab / read_tab tools so an agent can message or read another
tab by a git-style short handle (shortest unique prefix of the tab UUID,
min 4 chars), shown in the tab bar.

- core/db/tabs: resolveTabPrefix + shortestUniquePrefix (open tabs only,
  LIKE-sanitized prefix matching)
- new tools read-tab.ts / send-to-tab.ts (+ tests) decoupled from the DB
  TabRow via a minimal ResolvedTabRef projection
- agent-manager: unified deliverMessage routing (busy -> queue, idle ->
  new turn) shared by POST /chat and send_to_tab; agent->agent auto-wake
  budget (MAX_AGENT_AUTO_WAKES) to bound ping-pong loops
- summon/loader: send_to_tab + read_tab as grantable tools
- frontend: shortHandleFor + handle badge in TabBar; perm toggles
- notes: tab-comm / user-agents / todo-redesign plans
- chore: biome format fixes (debug-logger, summon.test)

Refs notes/plan-tab-comm.md

1 files changed, 11 insertions, 0 deletions

diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index a3816ea..b1b17cc 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -49,6 +49,10 @@ export {
 	createTab,
 	getTab,
 	listOpenTabs,
+	MIN_TAB_PREFIX_LENGTH,
+	type ResolveTabPrefixResult,
+	resolveTabPrefix,
+	shortestUniquePrefix,
 	type TabRow,
 	updateTabModel,
 	updateTabStatus,
@@ -78,9 +82,16 @@ export { prefix as bashArityPrefix } from "./tools/bash-arity.js";
 export { createListFilesTool } from "./tools/list-files.js";
 export { createReadFileTool } from "./tools/read-file.js";
 export { createReadFileSliceTool } from "./tools/read-file-slice.js";
+export { createReadTabTool, type ReadTabCallbacks } from "./tools/read-tab.js";
 export { createToolRegistry } from "./tools/registry.js";
 export { createRetrieveTool, type RetrieveCallbacks } from "./tools/retrieve.js";
 export { BackgroundShellStore, createRunShellTool } from "./tools/run-shell.js";
+export {
+	createSendToTabTool,
+	type ResolvedTabRef,
+	type SendToTabCallbacks,
+	type TabResolution,
+} from "./tools/send-to-tab.js";
 export { analyzeCommand } from "./tools/shell-analyze.js";
 export {
 	type AvailableAgent,