feat: PM-Agent also need to look at PR comments

From Gitea issue #116.

Authored by the PM agent's worker; the merge gate is the approver. Refs #116.

Agent: pm-agent (issue #116, mode implement)

platform/pm-agent/configmap.yaml

@@ -129,6 +129,59 @@ data:
   # runbooks/pm-agent.md.
   PM_DRY_RUN: "false"
 
+  # --- mentions on a pull request (issue #116) --------------------------------
+  # OFF. Turning it on makes the dispatcher also look at PULL REQUESTS: a mention of the bot
+  # account in a pull request's conversation, or inside an inline review thread, makes the PM
+  # read that pull request and reply in that same thread, and follow-up comments in a thread
+  # that already holds a mention continue the conversation with no new mention. It can ONLY
+  # reply — a mention cannot start, revise or push a branch; that is the second half of
+  # issue #116 and has its own issue.
+  #
+  # WHY IT SHIPS OFF. Not one call on this path has been made against the live Gitea — the
+  # branch that wrote it held no Gitea credential and no cluster — and the cheap mention
+  # query it prefers needs a token scope the bot does not have today (see
+  # PM_PR_MENTION_DISCOVERY). The intended order is: set PM_PLAN once and read what it would
+  # have replied to, then set this to "true". Both are ConfigMap edits plus a
+  # config-generation bump.
+  PM_PR_MENTIONS: "false"
+
+  # How candidate pull requests are found. `auto` tries Gitea's notification list for the bot
+  # account first — one bounded call, which is the "way to check for '@'s for the bot account
+  # instead of scouring the entire pull request list" the operator asked for — and falls back
+  # to listing open pull requests if that is refused. `notifications` uses only the cheap
+  # query and does nothing if it is unavailable (it will not silently widen into the scan the
+  # operator rejected). `pulls` never calls the notification endpoint.
+  #
+  # EXPECT THE FALLBACK AT FIRST. Gitea puts /api/v1/notifications behind its own
+  # `notification` token scope, and the bot's token is minted
+  # `read:user, write:repository, write:issue, read:package` — so until the operator re-mints
+  # it with `read:notification`, the cheap query is refused and the dispatcher logs exactly
+  # that, naming the scope. Which query answered is logged every cycle either way.
+  PM_PR_MENTION_DISCOVERY: "auto"
+
+  # How far back the notification query looks. Longer costs nothing but a bigger response;
+  # shorter risks missing a mention the dispatcher was down for. A day is well inside the
+  # idempotency marker's reach, which does not expire at all.
+  PM_PR_NOTIFICATION_LOOKBACK_SECONDS: "86400"
+
+  # The same throttle shape as the issue path: one decision per pull request per cooldown
+  # window, and at most this many replies per poll.
+  PM_PR_COOLDOWN_SECONDS: "900"
+  PM_PR_MAX_REPLIES_PER_CYCLE: "1"
+
+  # How much of the change the PM is shown. The changed-file summary is always included; this
+  # caps the diff quoted beneath it. Set to "0" to send the file list alone — the right
+  # setting if the diffs here turn out to dominate the decision's token cost.
+  PM_PR_DIFF_MAX_CHARS: "20000"
+  PM_PR_MAX_CHANGED_FILES: "200"
+
+  # Plan mode for the pull-request path: discover, assemble the payload, PRINT it to the
+  # dispatcher's stdout, ask no model and post nothing. Setting it also enables the path, so
+  # it is one knob to look before leaping. PM_DRY_RUN above implies it, because on this path
+  # the posted reply IS the action under test and also the marker that changes future
+  # behaviour — posting it would make a dry run not dry.
+  PM_PLAN: "false"
+
   # If the gate refuses a worker's change, the branch is NOT pushed by default and the issue
   # gets the gate log instead. Set to "true" to push anyway and open a red pull request —
   # useful when a human wants to see the work, noisy as a standing setting.