ref(autofix): Gate manual PR iteration behind its own feature flag

[alexsohn1126]

Backend half of CW-1778. Frontend follows in a separate PR (static/ and src/ aren't atomically deployed); this lands first.

Why

organizations:autofix-pr-iteration currently gates both manual and automated CI PR iteration. That means we can't roll out automated CI iteration without also exposing the manual flow. This adds organizations:autofix-pr-iteration-manual (api_expose=True, the frontend needs it) and moves the human-triggered entry points onto it, leaving automated CI iteration on the existing flag.

Moved to -manual

Site	Gates
group_ai_autofix.py:358	the pr_iteration POST gate — only reachable from the drawer feedback form; automated CI iteration enters via the check_suite listener, not this endpoint
pr_iteration/mention.py:88	@sentry <feedback> PR comment trigger
pr_iteration/listeners/review.py:145	PR review / inline review comment trigger
autofix_agent.py:887	the "Comment @sentry <feedback>…" PR description footer
on_completion_hook.py:252	👀->🎉 reaction swap on the triggering comment

Accepts either flag

Two sites sit on the shared path and would have broken automated CI iteration if moved outright — the check_suite listener reaches both via trigger_consume_pr_iteration_feedback -> trigger_autofix_agent(step=PR_ITERATION):

• autofix_agent.py:416 — pr_iteration_enabled, which raises PrIterationNotEnabledException for any PR_ITERATION step
• agent/client.py:359 — the enable_pr_context_tools permission check, set from is_iteration_step for both flows

New response field

pr_iteration_enabled keeps its existing meaning (automated CI iteration). Manual state is reported by a new additive field, manual_pr_iteration_enabled, rather than by redefining the old one — an unread field today is one a future reader would misinterpret. test_get_reports_iteration_flags_independently pins all four flag combinations.

Unchanged

The automated CI entry point (pr_iteration/listeners/check_suite.py) has no autofix-pr-iteration check of its own; its sub-features already use separate flags (-review-request, -cap-assign).

Rollout

Orgs currently on autofix-pr-iteration keep automated CI iteration and lose manual iteration until autofix-pr-iteration-manual is enabled for them — enable the new flag for the existing org set before/with this deploy to keep behavior identical. Flagpole YAML lives in sentry-options-automator.

Tests

Manual-gate tests moved to the new flag. Three things worth calling out, each verified by mutation testing rather than assumed — in every case I widened the gate back to the coupled behavior and confirmed the test fails:

• The feature_disabled tests were vacuous. They relied on both flags defaulting off, so they passed even with a manual gate mutated to also accept autofix-pr-iteration. Each now turns the automated flag on while manual is off, so the assertion is "automated CI iteration does not grant manual iteration."
• The flag swaps in the test_skips_* tests are load-bearing, not churn. Left on the old flag, the feature check short-circuits ahead of the condition each test targets: test_skips_when_not_iterate_command still passes when fed a valid @sentry fix it body, because the disabled feature is what stops dispatch. Swapping the flag is what keeps those assertions meaningful.
• Both response fields report independently, so the two flows can't be conflated by a future edit.

New coverage:

• test_pr_iteration_enabled_by_either_flag — neither flag raises PrIterationNotEnabledException; each flag alone enables the step. This exception had no coverage before.
• test_client_init_succeeds_when_manual_pr_ctx_tools_flag_enabled — PR context tools under the manual flag; the existing old-flag test now pins the automated path.
• test_get_reports_iteration_flags_independently — all four flag combinations for the two response fields.

274 passed across the touched files. 6 unrelated failures in test_issue_search.py / test_coding_agent_handoffs.py reproduce identically on a clean master tree (verified via git stash).

refs CW-1778

[linear-code]

CW-1778