fix: sync dev branch with main timeline/schema changes and remove stale providers

Forward-port main's timeline epoch tracking, projected window selection,
and schema updates into dev. Remove aider/amp/gemini providers and
provider-history-compatibility layers that are no longer needed.

packages/app/src/hooks/use-agent-initialization.test.ts

@@ -2,10 +2,11 @@ import { describe, expect, it } from "vitest";
 import { __private__ } from "./use-agent-initialization";
 
 describe("useAgentInitialization timeline request policy", () => {
-  it("uses committed tail bootstrap when history has not synced yet", () => {
+  it("uses canonical tail bootstrap when history has not synced yet", () => {
     expect(
       __private__.deriveInitialTimelineRequest({
         cursor: {
+          epoch: "epoch-1",
           seq: 42,
         },
         hasAuthoritativeHistory: false,
@@ -14,10 +15,11 @@ describe("useAgentInitialization timeline request policy", () => {
     ).toEqual({
       direction: "tail",
       limit: 200,
+      projection: "canonical",
     });
   });
 
-  it("uses committed tail bootstrap when cursor is missing", () => {
+  it("uses canonical tail bootstrap when cursor is missing", () => {
     expect(
       __private__.deriveInitialTimelineRequest({
         cursor: null,
@@ -27,13 +29,15 @@ describe("useAgentInitialization timeline request policy", () => {
     ).toEqual({
       direction: "tail",
       limit: 200,
+      projection: "canonical",
     });
   });
 
-  it("uses committed catch-up after the current cursor once history is synced", () => {
+  it("uses canonical catch-up after the current cursor once history is synced", () => {
     expect(
       __private__.deriveInitialTimelineRequest({
         cursor: {
+          epoch: "epoch-1",
           seq: 42,
         },
         hasAuthoritativeHistory: true,
@@ -41,8 +45,9 @@ describe("useAgentInitialization timeline request policy", () => {
       }),
     ).toEqual({
       direction: "after",
-      cursor: { seq: 42 },
+      cursor: { epoch: "epoch-1", seq: 42 },
       limit: 0,
+      projection: "canonical",
     });
   });
 
@@ -56,6 +61,7 @@ describe("useAgentInitialization timeline request policy", () => {
     ).toEqual({
       direction: "tail",
       limit: 0,
+      projection: "canonical",
     });
   });