M3.3: the trust dial (the agent merges approved PRs)

A project's trust.merge is operator (the default) or approved (L3, D5,
#65). Set to approved, the harness, never the model, merges a PR in the
PR watch once an approving review from a gitea.operators account is on
its current commit, its checks pass (none at all counts; pending
waits) and it's mergeable; the item then goes on as after any merge.
Each reason to hold off (failed checks, conflicts, a refused merge) is
said once per commit.

Gitea enforces it: protection requires approvals from an operators-only
whitelist and dismisses stale ones. At start, for each approved
project, the agent checks by behaviour that its own unapproved merge is
refused, with a throwaway branch and PR made through the API (never the
workspace); if it isn't refused, the operator merges until a restart.

- gitea: approvals, combined check status, a PR's head commit and
  mergeability, API-made branches and their deletion.
- Test and bring-up repositories get the protection.
- Tests: the decision (unit), the hard wall on a real Gitea
  (test_trust_live), an e2e test where the operator only approves, and
  a walk property, merges_only_approved, checked against a mutant that
  ignores which commit was approved.

Closes #65

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPQ14L3LikyefCMFBqEbKE

nisse-dev/src/nisse_dev/config.py

@@ -67,7 +67,12 @@ PROJECT_OPTIONAL = (
     "labels",
     "secrets",
     "egress",
+    "trust.merge",
 )
+# The trust dial (L3, D5): who merges a project's PRs. "approved": the
+# harness merges once an operator approved the PR's current commit and its
+# checks pass, behind protection that requires that approval.
+MERGE_MODES = ("operator", "approved")
 # Who may see a project secret (D7, D8): the model's commands get it as an
 # environment variable, redacted from what comes back; harness-only ones are
 # never in a command the model chose.
@@ -315,6 +320,9 @@ def _parse_project(
         errors.append(f"{where}: set a push token or a push key, not both")
     labels = _strings(values.get("labels", []), f"{where}.labels", errors)
     egress = _strings(values.get("egress", []), f"{where}.egress", errors)
+    merge = str(values.get("trust.merge") or "operator")
+    if merge not in MERGE_MODES:
+        errors.append(f"{where}.trust.merge: must be one of {', '.join(MERGE_MODES)}")
     secrets = _parse_secrets(entry.get("secrets"), where, env, errors)
     return Project(
         name=name,
@@ -333,6 +341,7 @@ def _parse_project(
         labels=labels,
         secrets=secrets,
         egress=egress,
+        merge=merge,
     )
 
 
@@ -454,6 +463,7 @@ class Project:
     labels: tuple[str, ...] = ()  # added to every issue's own (D1)
     secrets: Mapping[str, Secret] = field(default_factory=dict)
     egress: tuple[str, ...] = ()  # beyond the default; recorded, not yet enforced
+    merge: str = "operator"  # the trust dial (L3): who merges its PRs
 
     def command_secrets(self) -> dict[str, str]:
         """The secrets the model's commands may see, by name."""

nisse-dev/src/nisse_dev/gitea.py

@@ -10,6 +10,7 @@ idempotent across a crash: boot reconciliation (L8) asks Gitea whether the
 effect already happened rather than repeating it.
 """
 
+import base64
 from dataclasses import dataclass
 from typing import Any
 
@@ -33,6 +34,18 @@ class PullRequest:
     head: str
     url: str
     merged: bool = False
+    head_sha: str = ""  # the commit the PR is at now
+    mergeable: bool | None = None  # None: Gitea didn't say
+
+
+@dataclass(frozen=True)
+class Approval:
+    """An approving review, and the commit it approved (L3: approvals bind
+    to exactly what was approved)."""
+
+    author: str
+    commit: str
+    stale: bool = False  # Gitea's mark: commits were pushed since
 
 
 @dataclass(frozen=True)
@@ -286,6 +299,47 @@ class GiteaClient:
                 break
         return when
 
+    def approvals(self, repo: str, index: int) -> list[Approval]:
+        """The PR's approving reviews that still stand: not dismissed."""
+        return [
+            Approval(
+                author=(review.get("user") or {}).get("login", ""),
+                commit=str(review.get("commit_id") or ""),
+                stale=bool(review.get("stale")),
+            )
+            for review in (
+                self._request("GET", f"/repos/{repo}/pulls/{index}/reviews") or []
+            )
+            if review.get("state") == "APPROVED" and not review.get("dismissed")
+        ]
+
+    def checks(self, repo: str, sha: str) -> str:
+        """A commit's combined check status: success, pending, failure or
+        error; "none" when no check reported on it at all."""
+        data = self._request("GET", f"/repos/{repo}/commits/{sha}/status") or {}
+        if not data.get("total_count") and not data.get("statuses"):
+            return "none"
+        return str(data.get("state") or "pending")
+
+    def branch_with_file(
+        self, repo: str, *, base: str, branch: str, path: str, text: str, message: str
+    ) -> None:
+        """A new branch off ``base`` with one file added, made through the
+        API: no clone, no workspace."""
+        self._request(
+            "POST",
+            f"/repos/{repo}/contents/{path}",
+            json={
+                "content": base64.b64encode(text.encode()).decode(),
+                "message": message,
+                "branch": base,
+                "new_branch": branch,
+            },
+        )
+
+    def delete_branch(self, repo: str, name: str) -> None:
+        self._request("DELETE", f"/repos/{repo}/branches/{name}")
+
     def repository(self, repo: str) -> dict[str, Any]:
         """The repository as this account sees it, permissions included."""
         return dict(self._request("GET", f"/repos/{repo}"))
@@ -320,6 +374,8 @@ def _pull_request(data: dict[str, Any]) -> PullRequest:
         head=(data.get("head") or {}).get("ref", ""),
         url=data.get("html_url", ""),
         merged=bool(data.get("merged")),
+        head_sha=(data.get("head") or {}).get("sha", ""),
+        mergeable=data.get("mergeable"),
     )
 
 

nisse-dev/src/nisse_dev/loop/agent.py

@@ -42,7 +42,7 @@ from nisse_dev.config import GENERAL
 from nisse_dev.delegation import DELEGATION_INTENT, Delegation
 from nisse_dev.expert import BudgetExhausted, ExpertDesk
 from nisse_dev.git import GitError
-from nisse_dev.gitea import GiteaClient, GiteaError, Issue
+from nisse_dev.gitea import GiteaClient, GiteaError, Issue, PullRequest
 from nisse_dev.llm import LLMError, RoleMap
 from nisse_dev.loop.actions import classify
 from nisse_dev.loop.classifier import IN_SCOPE, ActionClassifier, Scope
@@ -227,6 +227,8 @@ class Project:
     workspace: Workspace | None = None
     milestones: Milestones | None = None
     labels: tuple[str, ...] = ()
+    base: str = "main"
+    merge: str = "operator"  # the trust dial (L3): who merges its PRs
 
 
 def _restatement_problem(args: dict[str, object]) -> str | None:
@@ -297,6 +299,9 @@ class LoopAgent:
         self._helpers = helpers
         # L4: judges what the fast path doesn't know; without one, it runs.
         self._classifier = classifier
+        # The trust dial (M3.3): projects whose protection was checked, and
+        # whether the harness may merge their approved PRs.
+        self._merging: dict[str, bool] = {}
         # Verdicts by (item, agreed revision, action): judged once (M3.2).
         self._judged: dict[tuple[str, int, str], tuple[Verdict, tuple[str, str]]] = {}
         self._clock = clock
@@ -385,6 +390,9 @@ class LoopAgent:
         """Resume waiting points as they were, and never resume interrupted
         work blindly: an item cut off mid-run waits on the operator."""
         self._store.set_active(None, cause="boot")
+        for project in self._projects.values():
+            if project.merge == "approved":
+                self._may_merge(project)  # D4: verified at start, not assumed
         self._reconcile_publishing()
         self._reconcile_filing()
         self._reconcile_delegations()
@@ -408,6 +416,126 @@ class LoopAgent:
                         thread=loop.thread,
                     )
 
+    # -- the trust dial (L3, D5; M3.3) --------------------------------------------
+
+    def _merge_if_approved(
+        self, item: WorkItem, loop: Loop, repo: str, pr: PullRequest
+    ) -> tuple[PullRequest, Loop]:
+        """Merge the PR when an operator approved its current commit and its
+        checks pass. Gitea enforces the approval (protection); this only
+        decides when to ask it. Each reason to hold off is said once."""
+        try:
+            approvals = self._gitea.approvals(repo, pr.number)
+            checks = self._gitea.checks(repo, pr.head_sha)
+        except GiteaError as exc:
+            self._oplog.emit("loop.watch_unavailable", cause=str(exc))
+            return pr, loop
+        by = [
+            a.author
+            for a in approvals
+            if a.author in self._gitea_operators
+            and a.commit == pr.head_sha
+            and not a.stale
+        ]
+        if not by:
+            return pr, loop
+        held = ""
+        if checks in ("failure", "error"):
+            held = f"its checks failed ({checks}), so I'll leave it unmerged"
+        elif checks not in ("success", "none"):
+            return pr, loop  # pending: wait for them
+        elif pr.mergeable is False:
+            held = "it has conflicts with the base branch, so I can't merge it"
+        elif not self._may_merge(self._at(item)):
+            return pr, loop  # protection unverified: said when checked
+        if not held:
+            try:
+                self._gitea.merge_pull_request(repo, pr.number)
+            except GiteaError as exc:
+                held = (
+                    f"Gitea refused my merge ({exc}); I'll try again, or you "
+                    "can merge it"
+                )
+            else:
+                self._fact(item, f"merged PR #{pr.number} after {by[0]}'s approval")
+                self._transport.post(
+                    f"Merged PR #{pr.number} after {by[0]}'s approval.",
+                    thread=loop.thread,
+                )
+                return replace(pr, merged=True, state="closed"), loop
+        mark = f"{pr.head_sha}:{held}"
+        if loop.merge_held != mark:
+            self._transport.post(
+                f"{by[0]} approved PR #{pr.number}, but {held}.", thread=loop.thread
+            )
+            loop = replace(loop, merge_held=mark)
+        return pr, loop
+
+    def _may_merge(self, project: Project) -> bool:
+        """D4: protection verified, not assumed. Once per start, a check
+        that Gitea refuses the agent's merge without an approval; if it
+        doesn't, the operator merges until it's fixed."""
+        if project.merge != "approved":
+            return False
+        if project.name not in self._merging:
+            problem = self._merge_protection_problem(project)
+            self._merging[project.name] = problem is None
+            self._oplog.emit(
+                "loop.merge_protection",
+                cause="start" if problem is None else problem,
+                project=project.name,
+                verified=problem is None,
+            )
+            if problem is not None:
+                self._transport.post(
+                    f"{project.repo} is set to have me merge approved PRs, but "
+                    f"{problem}. I'll leave merging to you until that's fixed "
+                    "and I've restarted."
+                )
+        return self._merging[project.name]
+
+    def _merge_protection_problem(self, project: Project) -> str | None:
+        """A throwaway branch and PR, made through the API (never the
+        workspace, which may hold an item's work): merging it must be
+        refused. Closed and deleted either way."""
+        branch = f"nisse-check-{uuid.uuid4().hex[:6]}"
+        try:
+            self._gitea.branch_with_file(
+                project.repo,
+                base=project.base,
+                branch=branch,
+                path=".nisse-merge-check",
+                text="Checks that merging needs an approval; never merged.\n",
+                message="nisse-dev: merge check",
+            )
+        except GiteaError as exc:
+            return f"I couldn't make a branch to check merging: {exc}"
+        pr = None
+        try:
+            pr = self._gitea.open_pull_request(
+                project.repo,
+                head=branch,
+                base=project.base,
+                title="nisse-dev merge check (never merged)",
+                body="Checks that merging needs an approval; closed straight away.",
+            )
+            try:
+                self._gitea.merge_pull_request(project.repo, pr.number)
+            except GiteaError:
+                return None  # refused, as it should be
+            return (
+                f"I could merge my own PR #{pr.number} without an approval "
+                f"(it added .nisse-merge-check to {project.base})"
+            )
+        except GiteaError as exc:
+            return f"I couldn't open a PR to check merging: {exc}"
+        finally:
+            if pr is not None:
+                with contextlib.suppress(GiteaError):
+                    self._gitea.close_pull_request(project.repo, pr.number)
+            with contextlib.suppress(GiteaError):
+                self._gitea.delete_branch(project.repo, branch)
+
     def _reconcile_delegations(self) -> None:
         """L8, L9: a delegation cut off by a crash is discarded, its branch
         deleted and the milestone's left as it was. The item, cut off mid-
@@ -613,6 +741,15 @@ class LoopAgent:
                     )
                     new = True
             position = item.position
+            if (
+                not pr.merged
+                and pr.state == "open"
+                and not new
+                and item.position == WAITING
+                and loop.wait == MERGE
+                and self._at(item).merge == "approved"
+            ):
+                pr, loop = self._merge_if_approved(item, loop, repo, pr)
             if pr.merged:
                 self._fact(item, f"PR #{loop.pr} merged")
                 loop, position = replace(loop, pr=0, pr_url="", branch=""), READY

nisse-dev/src/nisse_dev/loop/build.py

@@ -230,6 +230,8 @@ def project_runtime(
         name=entry.name,
         repo=entry.repo,
         labels=entry.labels,
+        base=entry.base_branch,
+        merge=entry.merge,
         workspace=Workspace(
             host,
             entry.workspace,

nisse-dev/src/nisse_dev/loop/items.py

@@ -74,6 +74,9 @@ class Loop:
     # exactly that action, by its key).
     pending_action: str = ""
     allowed: str = ""
+    # The trust dial (M3.3): why an approved PR was last left unmerged, so
+    # it's said once per commit and reason.
+    merge_held: str = ""
 
     def to_data(self) -> dict[str, Any]:
         return asdict(self)

nisse-dev/tests/test_config.py

@@ -511,3 +511,10 @@ def test_capability_profiles_are_read() -> None:
 def test_a_bad_profile_is_reported() -> None:
     with pytest.raises(ConfigError, match="profiles.m.colour: unknown setting"):
         build(profiles={"m": {"colour": "red"}})
+
+
+def test_the_trust_dial_defaults_to_the_operator_merging() -> None:
+    assert only(build()).merge == "operator"
+    assert only(build(**{f"{P}trust__merge": "approved"})).merge == "approved"
+    with pytest.raises(ConfigError, match="trust.merge: must be one of operator"):
+        build(**{f"{P}trust__merge": "always"})

nisse-dev/tests/test_gitea.py

@@ -248,3 +248,74 @@ def test_assigned_at_is_the_last_assignment_across_pages() -> None:
 
     assert client(handler).assigned_at("o/r", 6, "dev-agent") == "t4"
     assert client(handler).assigned_at("o/r", 6, "nobody") is None
+
+
+def test_approvals_are_the_standing_approving_reviews() -> None:
+    reviews = [
+        {"state": "APPROVED", "user": {"login": "don"}, "commit_id": "abc"},
+        {
+            "state": "APPROVED",
+            "user": {"login": "don"},
+            "commit_id": "old",
+            "stale": True,
+        },
+        {
+            "state": "APPROVED",
+            "user": {"login": "x"},
+            "commit_id": "abc",
+            "dismissed": True,
+        },
+        {"state": "REQUEST_CHANGES", "user": {"login": "don"}, "commit_id": "abc"},
+        {"state": "COMMENT", "user": {"login": "don"}, "commit_id": "abc"},
+    ]
+    handler = lambda request: httpx.Response(200, json=reviews)
+    approvals = client(handler).approvals("o/r", 3)
+    assert [(a.author, a.commit, a.stale) for a in approvals] == [
+        ("don", "abc", False),
+        ("don", "old", True),
+    ]
+
+
+def test_checks_are_the_combined_status_or_none() -> None:
+    def handler(request: httpx.Request) -> httpx.Response:
+        assert request.url.path == "/api/v1/repos/o/r/commits/abc/status"
+        return httpx.Response(200, json=answer)
+
+    answer: dict = {"state": "", "total_count": 0, "statuses": []}
+    assert client(handler).checks("o/r", "abc") == "none"
+    answer = {"state": "pending", "total_count": 1, "statuses": [{}]}
+    assert client(handler).checks("o/r", "abc") == "pending"
+    answer = {"state": "success", "total_count": 2, "statuses": [{}, {}]}
+    assert client(handler).checks("o/r", "abc") == "success"
+
+
+def test_a_pull_request_carries_its_head_commit_and_mergeability() -> None:
+    data = {
+        **pr_json(5, "m-1"),
+        "head": {"ref": "m-1", "sha": "f00"},
+        "mergeable": True,
+    }
+    pr = client(lambda request: httpx.Response(200, json=data)).pull_request("o/r", 5)
+    assert (pr.head_sha, pr.mergeable) == ("f00", True)
+
+
+def test_a_check_branch_is_made_through_the_api() -> None:
+    seen: list = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        seen.append((request.method, request.url.path, request.content))
+        return httpx.Response(201, json={})
+
+    gitea = client(handler)
+    gitea.branch_with_file(
+        "o/r", base="main", branch="chk", path="f", text="x", message="m"
+    )
+    gitea.delete_branch("o/r", "chk")
+    body = json.loads(seen[0][2])
+    assert (seen[0][0], seen[0][1]) == ("POST", "/api/v1/repos/o/r/contents/f")
+    assert (body["branch"], body["new_branch"], body["content"]) == (
+        "main",
+        "chk",
+        "eA==",
+    )
+    assert seen[1][:2] == ("DELETE", "/api/v1/repos/o/r/branches/chk")

nisse-dev/tests/test_loop_milestones.py

@@ -14,7 +14,14 @@ from nisse_dev.cancel import Cancel
 from nisse_dev.canonical import ToolCall
 from nisse_dev.execution import SSHHost
 from nisse_dev.git import GitRepo
-from nisse_dev.gitea import Comment, GiteaError, Issue, PullRequest, ReviewNote
+from nisse_dev.gitea import (
+    Approval,
+    Comment,
+    GiteaError,
+    Issue,
+    PullRequest,
+    ReviewNote,
+)
 from nisse_dev.loop.agent import LoopAgent
 from nisse_dev.loop.driver import Driver
 from nisse_dev.loop.items import ANSWER, MERGE, WAITING, loop_of
@@ -62,6 +69,10 @@ class Forge:
         self.deps: dict[int, list[int]] = {}  # issue -> the issues it depends on
         self.assigned: list[int] = []  # issues the agent assigned to itself
         self.reassigned: dict[int, str] = {}  # issue -> when assigned again
+        # The trust dial (M3.3): reviews, check statuses, merges by the agent.
+        self.approved: dict[int, list[Approval]] = {}
+        self.status: dict[str, str] = {}  # commit -> combined check state
+        self.agent_merged: list[int] = []
 
     # intake
     def assigned_issues(self, repo: str, assignee: str) -> list[Issue]:
@@ -91,7 +102,40 @@ class Forge:
     # PRs
     def _pr(self, n: int) -> PullRequest:
         p = self.prs[n]
-        return PullRequest(n, p["state"], p["head"], f"https://g/pr/{n}", p["merged"])
+        return PullRequest(
+            n,
+            p["state"],
+            p["head"],
+            f"https://g/pr/{n}",
+            p["merged"],
+            head_sha=self.head_sha(n),
+        )
+
+    def head_sha(self, n: int) -> str:
+        ref = f"refs/heads/{self.prs[n]['head']}"
+        found = subprocess.run(
+            ["git", "--git-dir", str(self.bare), "rev-parse", "--verify", "-q", ref],
+            capture_output=True,
+            text=True,
+            check=False,
+        )
+        return found.stdout.strip()
+
+    def approve(self, n: int, by: str = "don", sha: str = "") -> None:
+        """A review approving the PR as it is now (or at ``sha``)."""
+        self.approved.setdefault(n, []).append(Approval(by, sha or self.head_sha(n)))
+
+    def approvals(self, repo: str, index: int) -> list[Approval]:
+        return self.approved.get(index, [])
+
+    def checks(self, repo: str, sha: str) -> str:
+        return self.status.get(sha, "none")
+
+    def branch_with_file(self, repo: str, *, base, branch, path, text, message) -> None:
+        git("--git-dir", str(self.bare), "update-ref", f"refs/heads/{branch}", base)
+
+    def delete_branch(self, repo: str, name: str) -> None:
+        git("--git-dir", str(self.bare), "update-ref", "-d", f"refs/heads/{name}")
 
     def find_pull_request(self, repo: str, head: str) -> PullRequest | None:
         for n, p in self.prs.items():
@@ -150,8 +194,15 @@ class Forge:
         return {"protected": self.protected, "user_can_push": not self.protected}
 
     def merge_pull_request(self, repo: str, index: int) -> None:
-        if self.protected:
+        """As protection would have it: an operator's approval of the
+        PR's current commit, or no merge."""
+        head = self.head_sha(index)
+        if self.protected and not any(
+            a.author == "don" and a.commit == head and not a.stale
+            for a in self.approved.get(index, [])
+        ):
             raise GiteaError("gitea POST merge returned 405: approvals needed")
+        self.agent_merged.append(index)
         self.merge(index)
 
     # what the operator does in Gitea

nisse-dev/tests/test_loop_properties.py

@@ -243,8 +243,33 @@ class Walk:
         self.steps: list[str] = []
         self.shown_at_go: list[str] = []  # item:revision on screen at each go
         self.now = 1000.0
+        # The trust dial (M3.3): half the walks have the agent merge approved
+        # PRs, behind protection that refuses anything else.
+        self.merge = "approved" if seed % 2 == 0 else "operator"
+        self.agent_merges: list[tuple[int, bool]] = []  # (PR, approved at head)
+        if self.merge == "approved":
+            for w in worlds.values():
+                self._watch_merges(w["forge"])
         self.agent, self.transport = self._agent()
 
+    def _watch_merges(self, forge: Forge) -> None:
+        """Protected, and each merge the agent asks for recorded with
+        whether an operator had approved the PR as it was."""
+        forge.protect()
+        merge = forge.merge_pull_request
+
+        def recorded(repo: str, index: int) -> None:
+            if not forge.prs[index]["head"].startswith("nisse-check-"):
+                head = forge.head_sha(index)
+                approved = any(
+                    a.author == "don" and a.commit == head and not a.stale
+                    for a in forge.approved.get(index, [])
+                )
+                self.agent_merges.append((index, approved))
+            merge(repo, index)
+
+        forge.merge_pull_request = recorded  # type: ignore[method-assign]
+
     def reads_yes(self, proposal: str, reply: str) -> bool:
         """The scripted go-ahead reader: a plain yes usually reads as one,
         and nothing else ever does."""
@@ -270,6 +295,7 @@ class Walk:
                     repo=w["repo_name"],
                     workspace=Workspace(w["host"], w["repo"].root, timeout_s=30),
                     milestones=w["milestones"],
+                    merge=self.merge,
                 )
                 for name, w in self.worlds.items()
             ],
@@ -342,6 +368,8 @@ class Walk:
                 weights.update(
                     {"comment": 4, "merge": 2, "close-pr": 1, "comment-merge": 2}
                 )
+                if self.merge == "approved":
+                    weights.update({"approve": 4})
         action = self.rng.choices(list(weights), list(weights.values()))[0]
         self.steps.append(f"{action}{self.name(item)}" if item else action)
         if action == "intake":
@@ -455,6 +483,16 @@ class Walk:
             self.agent.watch()
             forge.merge(loop.pr)
             self.agent._schedule()
+        elif action == "approve" and loop and forge.prs[loop.pr]["state"] == "open":
+            # An operator's approval, or someone else's; of the PR as it is,
+            # or of an earlier commit.
+            forge.approve(
+                loop.pr,
+                by=self.rng.choice(["don", "don", "mallory"]),
+                sha=self.rng.choice(["", "0" * 40]),
+            )
+            self.agent.watch()
+            self.agent._schedule()
         elif action == "merge" and loop and forge.prs[loop.pr]["state"] == "open":
             forge.merge(loop.pr)
             self.agent.watch()
@@ -497,6 +535,10 @@ class Walk:
 
     def check(self) -> None:
         where = f"seed {self.seed}, steps {self.steps}"
+        # D5: the agent asks Gitea to merge only what an operator approved
+        # as it is (Gitea would refuse the rest; the harness mustn't ask).
+        unapproved = [pr for pr, approved in self.agent_merges if not approved]
+        assert not unapproved, f"merges_only_approved: {unapproved}: {where}"
         self._dangerous_only_when_allowed(where)
         store = self.world["store"]
         items = self.items()

nisse-dev/tests/test_loop_trust.py

@@ -0,0 +1,187 @@
+"""The trust dial (L3, D5; M3.3): a project set to `merge: approved` has its
+PRs merged by the harness once an operator approved the PR's current commit
+and its checks pass. Gitea enforces the approval (protection); the agent
+checks at start that it does, and otherwise leaves merging to the operator."""
+
+import io
+from typing import Any
+
+from test_loop_milestones import (
+    DON,
+    FINISH,
+    RESTATE,
+    WORK,
+    Forge,
+    ScriptedModel,
+    call,
+    say,
+)
+from test_loop_milestones import item as the_item
+from test_loop_milestones import world as world  # noqa: PLC0414 -- the fixture
+
+from nisse_dev.cancel import Cancel
+from nisse_dev.loop.agent import LoopAgent, Project
+from nisse_dev.loop.driver import Driver
+from nisse_dev.loop.items import MERGE, loop_of
+from nisse_dev.oplog import OpLog
+from nisse_dev.tools import Workspace
+from nisse_dev.transport import InMemoryTransport
+from nisse_dev.worker import InlineWorker
+
+CLOSE = [call("close_item", summary="added and merged")]
+
+
+def agent_for(
+    world: dict[str, Any], model: ScriptedModel, merge: str = "approved"
+) -> tuple[LoopAgent, InMemoryTransport]:
+    transport = InMemoryTransport()
+    cancel = Cancel()
+    project = Project(
+        "sandbox",
+        "don/sandbox",
+        Workspace(world["host"], world["repo"].root, timeout_s=30),
+        world["milestones"],
+        merge=merge,
+    )
+    loop = LoopAgent(
+        world["store"],
+        transport,
+        world["forge"],
+        projects=[project],
+        account="nisse-dev",
+        operators={DON},
+        gitea_operators={"don"},
+        driver=Driver(model, "m", cancel=cancel),  # type: ignore[arg-type]
+        worker=InlineWorker(),
+        cancel=cancel,
+        oplog=OpLog("nisse-dev", io.StringIO()),
+    )
+    transport.on_message(loop.on_message)
+    return loop, transport
+
+
+def to_review(world: dict[str, Any], merge: str = "approved", *more: Any) -> Any:
+    """An item whose PR is up, waiting for the merge."""
+    world["forge"].protect()
+    model = ScriptedModel(RESTATE, [*WORK, *FINISH], *more)
+    agent, transport = agent_for(world, model, merge)
+    agent.boot()
+    agent.intake()
+    say(transport, world, "go")
+    item = the_item(world)
+    assert loop_of(item).wait == MERGE, (item.position, loop_of(item), said(transport))
+    return agent, transport
+
+
+def said(transport: InMemoryTransport) -> list[str]:
+    return [m.text for m in transport.outbound]
+
+
+def test_an_approved_pr_is_merged_and_the_item_goes_on(world: dict[str, Any]) -> None:
+    forge: Forge = world["forge"]
+    agent, transport = to_review(world, "approved", CLOSE)
+    pr = loop_of(the_item(world)).pr
+    agent.watch()
+    assert forge.agent_merged == []  # not approved yet
+    forge.approve(pr)
+    agent.watch()
+    agent._schedule()
+    assert forge.agent_merged == [pr]
+    assert f"Merged PR #{pr} after don's approval." in said(transport)
+    assert the_item(world).status == "closed"
+
+
+def test_the_operator_merges_by_default(world: dict[str, Any]) -> None:
+    forge: Forge = world["forge"]
+    agent, _ = to_review(world, "operator")
+    pr = loop_of(the_item(world)).pr
+    forge.approve(pr)
+    agent.watch()
+    assert forge.agent_merged == []
+    assert loop_of(the_item(world)).wait == MERGE
+
+
+def test_an_approval_of_an_older_commit_doesnt_count(world: dict[str, Any]) -> None:
+    forge: Forge = world["forge"]
+    agent, _ = to_review(world)
+    pr = loop_of(the_item(world)).pr
+    forge.approve(pr, sha="0" * 40)  # what the PR was before a fix
+    agent.watch()
+    assert forge.agent_merged == []
+
+
+def test_only_an_operators_approval_counts(world: dict[str, Any]) -> None:
+    forge: Forge = world["forge"]
+    agent, _ = to_review(world)
+    pr = loop_of(the_item(world)).pr
+    forge.approve(pr, by="mallory")
+    agent.watch()
+    assert forge.agent_merged == []
+
+
+def test_pending_checks_wait_and_failed_ones_are_said_once(
+    world: dict[str, Any],
+) -> None:
+    forge: Forge = world["forge"]
+    agent, transport = to_review(world)
+    pr = loop_of(the_item(world)).pr
+    forge.approve(pr)
+    forge.status[forge.head_sha(pr)] = "pending"
+    agent.watch()
+    assert forge.agent_merged == []
+    forge.status[forge.head_sha(pr)] = "failure"
+    agent.watch()
+    agent.watch()
+    held = [t for t in said(transport) if "its checks failed" in t]
+    assert len(held) == 1 and forge.agent_merged == []
+    forge.status[forge.head_sha(pr)] = "success"
+    agent.watch()
+    assert forge.agent_merged == [pr]
+
+
+def test_protection_is_checked_at_start(world: dict[str, Any]) -> None:
+    forge: Forge = world["forge"]
+    forge.protect()
+    agent, transport = agent_for(world, ScriptedModel())
+    agent.boot()
+    assert agent._merging == {"sandbox": True}
+    # The check's branch and PR are gone again.
+    assert all(p["state"] == "closed" for p in forge.prs.values())
+    assert forge.agent_merged == []
+    assert not [t for t in said(transport) if "leave merging to you" in t]
+
+
+def test_unprotected_means_the_operator_merges(world: dict[str, Any]) -> None:
+    forge: Forge = world["forge"]  # not protected: the agent could merge anything
+    model = ScriptedModel(RESTATE, [*WORK, *FINISH])
+    agent, transport = agent_for(world, model)
+    agent.boot()
+    assert agent._merging == {"sandbox": False}
+    assert any("I could merge my own PR" in t for t in said(transport))
+    agent.intake()
+    say(transport, world, "go")
+    pr = loop_of(the_item(world)).pr
+    forge.approve(pr)
+    agent.watch()
+    assert pr not in forge.agent_merged  # left to the operator
+
+
+def test_a_refused_merge_is_said_once_and_left_to_the_operator(
+    world: dict[str, Any],
+) -> None:
+    from nisse_dev.gitea import GiteaError
+
+    forge: Forge = world["forge"]
+    agent, transport = to_review(world)
+    pr = loop_of(the_item(world)).pr
+    forge.approve(pr)
+
+    def refuse(repo: str, index: int) -> None:
+        raise GiteaError("gitea POST merge returned 405: not mergeable")
+
+    forge.merge_pull_request = refuse  # type: ignore[method-assign]
+    agent.watch()
+    agent.watch()
+    refused = [t for t in said(transport) if "Gitea refused my merge" in t]
+    assert len(refused) == 1
+    assert loop_of(the_item(world)).wait == MERGE