fix(route): resume an existing ai/issue-N branch instead of losing re-triggered work

When an agent was re-triggered on an issue that already had a branch/open PR, route.sh created a
fresh branch from main (git checkout -b), so the push back was rejected non-fast-forward and the new
commits were silently dropped (|| true) -- the run reported success and re-announced the stale PR,
but the work was gone (observed on issue #17 run #88). Resume the existing branch when it exists, so
new commits fast-forward onto it and update its PR; only branch from main when none exists.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/ai-agent.yml

@@ -1,6 +1,9 @@
 name: ai-agent
-# Thin caller so the agents work on THIS repo too (their own workflow). Same shared logic.
+run-name: "ai-agent · #${{ github.event.issue.number }}"   # quotes required: bare # starts a YAML comment
-# New issues opened by ffaerber auto-start @pm; @mention an agent in a comment to route on replies.
+# Standard caller for the shared AI-agent workflow (ffaerber/agents). Copy this file VERBATIM into
+# any repo that should get the agents — it is identical in every repo. All logic + scripts live in
+# agents/.gitea/workflows/; scripts are fetched from @main at run time. The `jobs.agent` wrapper is
+# required: a reusable (workflow_call) workflow can only be invoked from a caller job, not top-level.
 on:
   issue_comment:
     types: [created]

.gitea/workflows/scripts/route.sh

@@ -55,7 +55,13 @@ if [ -n "$IS_PR" ]; then                     # comment on a PR -> resume its bra
   ref=$(curl -s -H "Authorization: token $GT" "$API/pulls/$NUM" | jq -r .head.ref)
   git fetch origin "$ref" && git checkout "$ref"
   { echo "branch=$ref"; echo "new=false"; } >> "$GITHUB_OUTPUT"
-else                                         # comment on an issue -> new branch
+elif git ls-remote --exit-code --heads origin "ai/issue-$NUM" >/dev/null 2>&1; then
+  # comment on an issue whose branch ALREADY exists (a prior run / open PR) -> RESUME it, so new
+  # commits fast-forward onto the same branch and update its PR. Branching fresh from main here would
+  # be rejected on push as non-fast-forward and the new work would be silently lost (see issue #17).
+  git fetch origin "ai/issue-$NUM" && git checkout "ai/issue-$NUM"
+  { echo "branch=ai/issue-$NUM"; echo "new=false"; } >> "$GITHUB_OUTPUT"
+else                                         # comment on an issue, no branch yet -> new branch
   git checkout -b "ai/issue-$NUM"
   { echo "branch=ai/issue-$NUM"; echo "new=true"; } >> "$GITHUB_OUTPUT"
   # For dev agents, publish the branch immediately and tell the maintainer where to watch.

README.md

@@ -29,10 +29,18 @@ detail out of agents that shouldn't act on it while still letting them know the
 
 ## Use it in a repo
 
-Add `.gitea/workflows/ai-agent.yml` to the consuming repo:
+**The standard caller is one file, identical in every repo.** Copy this repo's own
+[`.gitea/workflows/ai-agent.yml`](.gitea/workflows/ai-agent.yml) verbatim into the consuming repo —
+it is the source of truth, and `agents` itself uses the same file:
 
 ```yaml
 name: ai-agent
+run-name: "ai-agent · #${{ github.event.issue.number }}"   # quotes required: bare # starts a YAML comment
+# Standard caller for the shared AI-agent workflow (ffaerber/agents). Copy this file VERBATIM into
+# any repo that should get the agents — it is identical in every repo. All logic + scripts live in
+# agents/.gitea/workflows/; scripts are fetched from @main at run time. The `jobs.agent` wrapper is
+# required: a reusable (workflow_call) workflow can only be invoked from a caller job, not top-level.
+# `run-name` titles each run by the triggering issue (e.g. "ai-agent · #42") in the Actions list.
 on:
   issue_comment:
     types: [created]
@@ -44,7 +52,9 @@ jobs:
     secrets: inherit
 ```
 
-That's the whole per-repo footprint. All the logic (agent registry, routing, delegation,
+That's the whole per-repo footprint, and it's the minimum a caller can be: the `on:` triggers must
+live in each repo (a reusable workflow can't declare its callers' triggers) and the `jobs.agent`
+wrapper is mandatory for `workflow_call`. Everything else (agent registry, routing, delegation,
 reactions, PR/issue plumbing) lives here in `agent.yml`.
 
 ## Repo layout