Board Program LEARN context, ruff 0.16, and verb-rejection observability (#700)

* fix(board): LEARN decisions name the item, not its per-cycle index

A cycle's reject reasons are rendered into the NEXT cycle's exploration
prompt, but the ref recorded alongside each reason was the item's stored
id (item-0/item-1) — a per-cycle index that means something different
every cycle and appears nowhere the explorer can resolve. The reason
survived the loop; what it was about did not.

Record the item's title instead, via a shared learn_ref() helper (falls
back to the id when title-less, and reads target_task_title for Scales,
whose items name the live task they mutate).

* chore(lint): satisfy ruff 0.16 — keyword-only signatures and markdown formatting

The dev toolchain resolved ruff 0.16.0, which stabilises PLR0917 (too many
positional arguments) and formats python code blocks inside markdown. Both
fired repo-wide and neither had anything to do with the code they flagged.

- 36 signatures gain a `*` so their tail arguments are keyword-only, and
  the 104 call sites that passed them positionally are converted. mypy was
  the safety net for the static ones; the full suite caught nine more that
  only bind at runtime (the MCP tool functions, whose real callers already
  pass named JSON arguments).
- 28 markdown files reformatted by 0.16's code-block formatter.
- One RUF036 (`None` mid-union) autofixed in the GitLab provider.

* fix(gateway): log the reason when a verb rejects

A rejected envelope rides an HTTP 200, its body is never logged, and there
is no trace table — so in the access log a verb an agent could not satisfy
looks identical to one that worked. On 2026-07-25 four Board Programs
(Periscope, Sentinel, Scales, Barfly) each POSTed their propose verb three
or four times, persisted nothing, and left their exploration tasks PENDING;
the reason was unrecoverable afterwards, from the logs or from the agents'
own transcripts.

Log error/message/remediate/missing plus the calling agent at
envelope_to_response — the one chokepoint every v1 flow and do route
returns through. Success envelopes stay silent.

---------

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

docs/rag/tools/a2a-tools.md

@@ -6,10 +6,10 @@ A2A is direct peer-to-peer messaging between agents. There is **no** `roboco_age
 
 ```python
 dm(
-    recipient="be-qa",          # target agent slug
+    recipient="be-qa",  # target agent slug
     text="Please review my changes",
-    task_id="abc123...",        # auto-filled from your active task if omitted
-    skill=None,                 # optional skill slug to scope the conversation
+    task_id="abc123...",  # auto-filled from your active task if omitted
+    skill=None,  # optional skill slug to scope the conversation
 )
 ```
 
@@ -37,7 +37,7 @@ Same-cell peers (e.g. `be-dev-1` alongside `be-dev-2`/`be-qa`/`be-doc`/`be-pm`)
 When another agent messages you, your claim briefing surfaces it under `unread_a2a` — each entry shows the sender and a preview of their latest incoming message. To read the full bodies (and clear them), call:
 
 ```python
-read_a2a()      # -> {"messages": [{from_agent, content, created_at}, ...]}
+read_a2a()  # -> {"messages": [{from_agent, content, created_at}, ...]}
 ```
 
 `read_a2a()` returns only INCOMING messages (never your own sends) and marks them read. `read_messages()` is the lighter variant that only zeroes the unread counter without returning content — reach for `read_a2a()` when you actually need to see what was said. Either clears `i_am_idle()`'s unread-A2A soft-block.
@@ -45,9 +45,9 @@ read_a2a()      # -> {"messages": [{from_agent, content, created_at}, ...]}
 Formal, ack-required notifications are a separate inbox — see `docs/rag/tools/messaging-tools.md`:
 
 ```python
-notify_list(unread_only=True)   # list pending items
-notify_get(notification_id)     # read one (marks it read)
-notify_ack(notification_id)     # acknowledge after handling
+notify_list(unread_only=True)  # list pending items
+notify_get(notification_id)  # read one (marks it read)
+notify_ack(notification_id)  # acknowledge after handling
 ```
 
 ## When to use A2A