feat: emit tool-call file previews

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

ARCHITECTURE.md

@@ -220,6 +220,8 @@ The protocol also carries **turn-scoped lifecycle events** alongside output delt
 
 These events flow through a single `onTurnScopedEvent` callback on the `runTurn` command, avoiding per-event-type callback proliferation. The main process maps each event to a `SessionEventRecord` and pushes it to the renderer, where lightweight state maps (activity, usage, turn-event log) consume them without touching the persisted workspace.
 
+Tool-call activity records can also be enriched with a stable `toolCallId` and aggregated file-change preview payloads (`path`, unified diff, and optional new-file contents). The sidecar derives those previews from Copilot SDK write permission requests, and the main process merges repeated write events by `toolCallId` into the persisted run timeline so future UI surfaces can render file previews without reinterpreting approval payloads.
+
 The same boundary also supports server-scoped sidecar commands that do not require a live Copilot session. The new `get-quota` command uses the SDK's `account.getQuota` RPC to fetch account quota snapshots on demand, then returns them as a `quota-result` protocol event followed by the usual `command-complete` sentinel.
 
 For project-backed sessions, the sidecar also discovers GitHub Copilot CLI hook definitions from `.github/hooks/*.json` under the repository root. Those files are parsed and merged once per run bundle, then projected onto the SDK session hook delegates. Hook commands run synchronously in the sidecar through the platform shell, with stdin JSON payloads shaped to match Copilot CLI hook expectations as closely as the SDK allows. Hook failures are logged to stderr and treated as non-fatal diagnostics, while `preToolUse` hook outputs can still deny a tool call before Aryx falls back to its built-in approval policy.