feat(webui): request preview, authorization, and workflow initiation (Closes #643)

Operators had to paste a role prompt into a terminal to start work, and
nothing enforced that the allocator had been consulted first, so two sessions
could reach for the same issue and each believe it was theirs. This adds a
request surface: a desired role, an issue or PR, and a stated intent, answered
by an authorization decision and - on confirmation - an exclusive assignment
from the allocator.

Preview (POST /api/v1/requests/preview, and the /requests form) runs five
checks and reports authorize/deny with a reason for each: console
authorization, capability resolution for the desired role, lease availability,
whether the allocator would independently select this work unit, and head
pinning for PR work. It is read-only - it calls the allocator with apply=false
and writes only an audit line. An unauthorized principal never reaches the
allocator or the control-plane DB, so a denial cannot enumerate the queue.

Initiation (POST /api/v1/requests/apply) never assigns the requested item
directly. It runs a dry-run first and proceeds only when the allocator would
independently pick that exact work unit, carrying the dry-run's
candidate_set_fingerprint as a CAS pin; otherwise it returns wait or blocked
and mutates nothing. An active claim on the work unit rejects a duplicate
assign before one is attempted. A returned assignment carries a handoff block
naming the required profile, namespace, and the actions that stay forbidden.

Authorization reuses the #633 model rather than adding a second one. The new
initiate_workflow action is operator-class because its outcome is a claim, not
a Gitea verdict: requesting reviewer or merger work reserves that work but
grants no right to approve or merge. Execution is gated by a new per-action
execution_env_flag (WEBUI_REQUESTS_EXECUTION), deliberately in place of raising
ACTIVE_PHASE - a phase bump would enable execution for every phase-2 action at
once, including ones whose execution path is not implemented. Actions that
declare no flag are unchanged and still report execution_enabled false.

Every preview and apply emits a console audit record correlated to the
resulting assignment by correlation.request_id.

Fail-closed throughout: an unreadable control-plane DB, an incomplete queue
inventory (#758), an allocator that raises, an unpinned PR head, a moved PR
head, and an unconfirmed apply all deny without mutating.

Files:
- webui/request_service.py (new) - request model, preview, initiation
- webui/request_views.py (new) - form and preview rendering, escaped
- tests/test_webui_request_initiation.py (new) - 52 tests
- webui/console_authz.py - initiate_workflow action, execution_wired()
- webui/app.py - /requests, /api/v1/requests/preview, /api/v1/requests/apply
- webui/nav.py - Requests nav entry
- webui/traffic_loader.py - public candidates_from_queue_snapshot alias
- docs/webui-requests.md (new), docs/webui-authz-audit.md

Validation: full suite on this branch 5242 passed, 6 skipped, 899 subtests, 23
failed. Clean master baseline at 2f4dec83 in an equivalent branches/ worktree:
5190 passed, 6 skipped, 867 subtests, the same 23 tests failed. The branch adds
52 passing tests and introduces no new full-suite failure signature.

Closes #643

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

webui/console_authz.py

@@ -115,6 +115,12 @@ class ConsoleAction:
     break_glass: bool
     phase: int
     summary: str
+    # Opt-in switch for an action whose execution path is genuinely wired
+    # ahead of its phase becoming globally active (#643). Naming a variable
+    # here enables nothing on its own: the variable must also be set in the
+    # environment. An action that leaves this ``None`` can only execute once
+    # ACTIVE_PHASE reaches its phase, exactly as before.
+    execution_env_flag: str | None = None
 
     @property
     def mcp_permission(self) -> str:
@@ -277,6 +283,27 @@ _ACTION_SPECS: tuple[ConsoleAction, ...] = (
         phase=2,
         summary="Restart one MCP namespace via the host supervisor.",
     ),
+    # #643: submit a work request — desired role, issue/PR, intent — and let
+    # the allocator reserve it. This is the one Phase 2 action whose execution
+    # path is actually implemented (``webui.request_service``), so it carries
+    # the opt-in flag; it stays denied until an operator sets that variable.
+    # Authority is operator-class because the outcome is a claim, not a Gitea
+    # verdict: initiating reviewer or merger *work* does not grant the right
+    # to approve or merge, which stays with the MCP role profile.
+    ConsoleAction(
+        action_id="initiate_workflow",
+        task_key="allocate_next_work",
+        action_class=CLASS_WRITE,
+        minimum_role=OPERATOR,
+        requires_confirmation=True,
+        dual_control=False,
+        break_glass=False,
+        phase=2,
+        summary=(
+            "Preview and initiate allocator-owned workflow work for a role."
+        ),
+        execution_env_flag="WEBUI_REQUESTS_EXECUTION",
+    ),
 )
 
 ACTIONS: dict[str, ConsoleAction] = {a.action_id: a for a in _ACTION_SPECS}
@@ -430,6 +457,33 @@ ALLOW_PREVIEW = "allowed_preview_only"
 # gated on this model landing; nothing here enables it.
 ACTIVE_PHASE = 1
 
+_TRUTHY = frozenset({"1", "true", "yes", "on"})
+
+
+def execution_wired(
+    action: ConsoleAction | None, env: dict[str, str] | None = None
+) -> bool:
+    """Whether *action* has a live execution path right now.
+
+    Two ways to be wired, and only two. The action's phase is active, or the
+    action declares an opt-in environment variable *and* that variable is set.
+    Everything else — including every action that never declares a flag — is
+    unwired, so the default across the registry stays deny.
+
+    Bumping ``ACTIVE_PHASE`` would enable execution for every action of that
+    phase at once. The per-action flag exists so a single implemented action
+    can go live without dragging its unimplemented phase-mates with it.
+    """
+    if action is None:
+        return False
+    if action.phase <= ACTIVE_PHASE:
+        return True
+    flag = (action.execution_env_flag or "").strip()
+    if not flag:
+        return False
+    source = env if env is not None else os.environ
+    return (source.get(flag) or "").strip().lower() in _TRUTHY
+
 
 @dataclass(frozen=True)
 class AuthorizationDecision:
@@ -469,16 +523,19 @@ def authorize(
     principal: Principal | None = None,
     *,
     for_execution: bool = False,
+    env: dict[str, str] | None = None,
 ) -> AuthorizationDecision:
     """Decide whether *principal* may invoke *action_id*. Deny by default.
 
     ``for_execution`` distinguishes a read-only preview from a real invocation.
-    Even an allowed decision reports ``execution_enabled=False`` while the
-    console is in Phase 1, so no caller can read an allow as permission to
-    mutate.
+    ``execution_enabled`` reports whether the action has a live execution path
+    at all (:func:`execution_wired`) — for every action without an explicit
+    opt-in flag that stays ``False`` while the console is in Phase 1, so no
+    caller can read an allow as permission to mutate.
     """
     who = principal if principal is not None else ANONYMOUS
     action = get_action(action_id)
+    wired = execution_wired(action, env)
 
     if action is None:
         return AuthorizationDecision(
@@ -497,7 +554,7 @@ def authorize(
         "requires_confirmation": action.requires_confirmation,
         "dual_control": action.dual_control,
         "break_glass": action.break_glass,
-        "execution_enabled": False,
+        "execution_enabled": wired,
     }
 
     if not who.authenticated:
@@ -530,13 +587,19 @@ def authorize(
             **base,
         )
 
-    if for_execution and action.phase > ACTIVE_PHASE:
+    if for_execution and not wired:
         return AuthorizationDecision(
             allowed=False,
             reason_code=DENY_PHASE_NOT_ACTIVE,
             detail=(
                 f"Action {action_id!r} belongs to phase {action.phase}; the "
-                f"console is in phase {ACTIVE_PHASE}. Execution is not wired."
+                f"console is in phase {ACTIVE_PHASE}"
+                + (
+                    f" and {action.execution_env_flag} is not set"
+                    if action.execution_env_flag
+                    else ""
+                )
+                + ". Execution is not wired."
             ),
             **base,
         )
@@ -545,8 +608,8 @@ def authorize(
         allowed=True,
         reason_code=ALLOW_PREVIEW,
         detail=(
-            "Principal holds the required role. Preview only — execution "
-            "remains disabled until the Phase 2 action framework ships."
+            "Principal holds the required role. Execution proceeds only for an "
+            "action with a wired execution path; everything else is preview."
         ),
         **base,
     )