Local-model commits carry Co-Authored-By: <model> <agent@wntrmute.dev>

Owner's rule. The implementer often cannot know which model it is, so
run-plan.sh derives the name from OPENCODE_MODEL (the part after the
provider), gives the exact trailer and the Model column's value in the
session prompt, and stops the run when a task's commit lacks that exact
line. AGENTS.md replaces the old Implemented-By trailer and the "owner
fills in the model" rule.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -97,8 +97,10 @@ Useful while working: `cargo test -p <crate> --test <file>` runs one test file,
 - Work on the branch the task names. One task is one commit.
 - Stage only the paths the task lists: `git add <path> ...`. Never `git add -A` or `git add .`.
 - Never push, amend, rebase, reset, or switch to another branch.
-- Commit message: the subject line the task gives, a blank line, then this trailer:
-  `Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)`
+- Commit message: the subject line the task gives, a blank line, then the `Co-Authored-By` line
+  your session prompt gives, exactly, for example
+  `Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>`. If the prompt gives none, stop and
+  report.
 
 ## The implementer log
 
@@ -115,4 +117,4 @@ bad one.
 | First gate | `pass` or `fail` for the first run |
 | Deviations | Anything you did that the task did not say, or `none` |
 | Notes | Problems you hit and how you solved them, in one or two sentences |
-| Model | Write `?`. The owner fills this in. |
+| Model | The model name your session prompt gives (as in the `Co-Authored-By` line), or `?` if it gives none. |