refactor(webhook): extract prompt rendering into webhook_rendering mixin (Webhook Feature Package)

[andrexibiza]

Part of the Webhook Feature Package Feature Package.

Behavior-preserving verbatim extraction of the prompt-rendering cluster from gateway/platforms/webhook.py into gateway/platforms/webhook_rendering.py:

• _render_prompt (dot-notation payload access, {__raw__} truncation, {event_type})
• _render_delivery_extra (string template rendering, non-string passthrough)

Composed as WebhookRenderingMixin into WebhookAdapter MRO. Call sites resolve through the mixin.

Verification (57 passed)

• tests/gateway/test_webhook_rendering_seam.py — new seam test
• tests/gateway/test_webhook_adapter.py + test_webhook_signature_rate_limit.py + test_webhook_integration.py + test_webhook_dynamic_routes.py + test_webhook_deliver_only.py + test_webhook_profile_admission_seam.py — no behavior change
• git diff --check clean; webhook.py 1308 lines, webhook_rendering.py 60 lines (both < 2000)

5×2×3

Blind implementer + blind witness on this lane. Also made the profile admission seam test MRO-robust (assert membership + method identity instead of exact prefix) so adding further mixins does not break the seam contract.

Related #85054

[alt-glitch]

This was generated by AI during triage.

Related to #84835: this stacked extraction also drops multiplex_profile_allowlist when resolving served profiles. Please resolve that admission regression before this slice is merged; the rendering extraction remains complementary to #84849.

[Enough1122]

AI code review — automated review for reference, author can ignore or act on any point.

refactor(webhook): extract prompt rendering into webhook_rendering mixin (Webhook Feature Package)

Byte-identical extraction, and test_webhook_rendering_seam.py covers the real semantics rather than just the seam. Observations:

1. Truncation can emit invalid JSON inside template output — _render_prompt truncates serialized dict/list values at 2000 chars (json.dumps(value, indent=2)[:2000]), which can cut mid-string and produce a fenced block that is not parseable JSON. [SUPERSEDED by #90236] webhook Task 10 historical campaign lineage #85523 fixes the {__raw__} case with a structural envelope; consider applying the same envelope treatment to nested-value truncation so downstream parsers never receive a raw character slice.

2. Router extraction duplicated across the series — the hermes_cli/web_routers/webhooks.py + web_server.py change is identical in refactor(webhook): extract webhook API router + profile admission (Webhook Feature Package) #84835/refactor(webhook): extract signature validation into webhook_auth mixin (Webhook Feature Package) #84849/refactor(webhook): extract prompt rendering into webhook_rendering mixin (Webhook Feature Package) #84858/refactor(webhook): extract delivery into webhook_delivery mixin (Webhook Feature Package) #84939 against the same base; merge conflicts are guaranteed unless it lands once and the others rebase.

3. _render_delivery_extra does not recurse — string values are rendered as templates but nested dict/list values pass through unrendered; if a deliver_extra contains a nested {"repo": "{org}/x"} template, it is not expanded. Pre-existing behavior, but worth documenting since the extraction is the moment to write it down.

4. Good: the {__raw__} 4000-char cap and the missing-key passthrough ({key} literal) are preserved exactly.

[andrexibiza]

Decision recorded against current main 3a034356a237341452b7afebd3a2bfd21021609f and the live webhook train.

Do not land this old stacked head independently. The canonical order is:

1. refactor(webhook): extract webhook API router + profile admission (Webhook Feature Package) #84835 owns the REST-router/profile-admission extraction once; all duplicate router/profile commits must disappear from sibling branches.
2. Restack refactor(webhook): extract prompt rendering into webhook_rendering mixin (Webhook Feature Package) #84858 as a rendering-only extraction on that canonical base, preserving the multiplex allowlist fix and proving the MRO/seam.
3. refactor(webhook): isolate explicit provider signature authority #85318 carries the explicit signature contract and supersedes the older auth-extraction-only shape in refactor(webhook): extract signature validation into webhook_auth mixin (Webhook Feature Package) #84849.
4. Retarget [SUPERSEDED by #90236] webhook Task 10 historical campaign lineage #85523 onto the extracted owners and finish intake/idempotency/raw-payload behavior there.

That order makes webhook_rendering.py the canonical owner before Task 10 changes {__raw__:N}, total UTF-8 envelope bounds, nested-value structural truncation, and default-prompt rendering. It also prevents the same router extraction from landing four times.

The current 10-file head is not landable: it includes duplicated structural commits and preserves rendering behavior that Task 10 must change. Narrow, rebase in the order above, recompute the rendering golden window, then run the composed #85318/#85523 webhook matrix.