The forge announces every merge, whoever made it

The merge tool emitted at the instant it acted; a merge made in the forge's own
pages or over its API emitted nothing, and the mesh went on believing every module
current with its source (novox/hq 04-ISSUES/131). Merged pull requests are now
watched the way repositories are: what the forge holds, asked for on a tick,
announced once, with the merge commit and the clone URL a build needs. What has
been announced is kept beside the module's state, so a restart does not announce
the whole history again, and a first tick with no record announces nothing.

modules/gitea/tools/index.ts

@@ -231,6 +231,8 @@ export function getGiteaTools(gitea: GiteaClient): ToolDefinition[] {
         // Read the PR first, so the merged event carries a title and branches, not just a number.
         const pull = await gitea.getPullRequest(owner, repo, number);
         await gitea.mergePullRequest(owner, repo, number, method, deleteBranch);
+        // Read it again: the merge commit only exists now, and it is what a build is made from.
+        const merged = await gitea.getPullRequest(owner, repo, number);
         await emit("pull.merged", {
           owner,
           repo,
@@ -238,6 +240,8 @@ export function getGiteaTools(gitea: GiteaClient): ToolDefinition[] {
           title: pull.title,
           head: pull.head,
           base: pull.base,
+          merge_commit_sha: merged.merge_commit_sha,
+          merged_at: merged.merged_at,
           method,
           html_url: pull.html_url,
         });