Copy as code: copy a code-managed template as its HTML file #509

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1. Silthus

   added

   wayfinder:implement

   on Oct 17, 2026
2. Silthus

   added a parent issue on Oct 17, 2026

   • Map: send code-managed email templates with one PostHog call #461
3. Silthus

   marked this as blocked on Oct 17, 2026

   • Edit with your agent: copy a prompt for a code-managed template's file #503
4. Silthus

   marked this as blocking on Oct 17, 2026

   • Ship stack A: edit a code-managed template with your agent #516
5. Silthus

   self-assigned this

   on Oct 17, 2026
6. Silthus commented on Oct 17, 2026

   

   Silthus

   on Oct 17, 2026

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   Runtime: T3 child task
   Task: node:delegated-task:command%3Amcp%3A1778d880-5a25-404c-80d0-25fc5ccca3b2%3Adelegate-task%3Awf-email-impl-509-1
   Cast: Opus 5.5, high. Cap 180 minutes.
7. Silthus commented on Oct 17, 2026

   

   Silthus

   on Oct 17, 2026

   OwnerAuthor

   More actions

   Note

   🤖 Opus 5.5 responding on behalf of Michael

   Resolution

   Landed 8a50f6ef11c on spec/template-agent-edit as a fast-forward from 62c695af6cb. The ship ticket #516 owns the PR and the review.

   • Menu item: "Edit with your agent" is now a split button. Its side menu offers "Copy HTML file". The side button replaces the dropdown chevron, as Edit with your agent: copy a prompt for a code-managed template's file #503's follow-up asked.
   • Encoder (templateHtmlFile.ts, pure) turns the published subject, preheader and HTML into the file posthog.emails.templateFile() reads:
     • the subject goes into the first <title>. A missing title is added at the start of <head>, and a missing <head> is added too;
     • the preheader goes into the first <meta name="preheader">. A missing tag is added after the title;
     • a tag whose parsed value already matches stays byte for byte, so an author's é survives;
     • a blank preheader removes its tag;
     • Liquid stays literal, and nothing else is reformatted or reordered.
   • Toast: "Copied. Save it as the template's file. PostHog keeps sending the current version until your app sends or uploads the file." When the saved template has a nonempty text part, the toast adds "This file has no plain-text part. The next upload from this file removes the plain-text version." Copy is never blocked.
   • Event: message template html file copied {template_id, dropped_text_part}.
   • Story: Products/Workflows/Template library/Edit with your agent gains Copy menu open.

   Proof

   Red (red.log): the final test table against an encoder that always rewrites the title and meta. 1 failed, 10 passed. The failing case is gives back the file the SDK uploaded byte for byte: an author's own entities, whitespace and attribute order: the output loses Café and the author's single-quoted meta. The logic red (red-logic.log): TypeError: logic.actions.copyHtmlFile is not a function.

   Green (green.log): every suite under TemplateLibrary/ plus lib/components/Git on the landed tree. 8 suites, 101 passed, nothing skipped.

   Seam	Asserts
   templateHtmlFile: 3 files uploaded by the SDK	the encoder returns each file byte for byte. Rows: the research report's synthetic vector v1:b967355e…; an author's entities, whitespace and attribute order; a commented-out title before the real one, with no preheader
   templateHtmlFile: 8 encoded templates	exact output bytes; the SDK's recorded parse of those bytes equals the template's subject (whitespace collapsed) and preheader; encoding the output again changes nothing. Rows: missing head, missing title and meta, a bare fragment, escaped subject, escaped preheader, blank preheader, Liquid with quotes and >, a subject that matches after whitespace collapses
   messageTemplateLogic, API mocked at HTTP, with and without a text part	the clipboard holds the encoded file; no PATCH or POST; the exact toast; the event with dropped_text_part

   I recorded each row's expected parse and hash once with the SDK's own parseTemplateFile and emailContentHash, at PostHog/posthog-js#5312's head 87e9e95ca65 (script). The server's Python hash agrees on the SDK rows.

   Property check, not committed (script, result): 10,560 combinations of document shapes, subjects and preheaders. The cases include comments, an SVG <title>, entities, quotes, Liquid and blank values. For each, the real SDK parser read the encoded file back as the template's subject and preheader, and a second encode changed nothing. failed 0.

   Local gate on the landed tree:

   • tsgo --noEmit --checkers 1 in frontend/ through fleet heavy: exit 0 (log).
   • pnpm --filter=@posthog/frontend fix through fleet heavy: exit 0, no further changes.
   • kea typegen on messageTemplateLogic.ts matches the committed inline types.
   • The pre-push hook (hogli ci:preflight --strict): "failures": 0 (log).
   • No backend change, so no build:openapi or mypy run.

   Browser round trip (Storybook from this worktree, real App scene, API mocked at HTTP, headless Chromium with clipboard access, log):

   • SDK upload: the template served exactly the fields posthog-node uploads for this file: parseTemplateFile's subject and preheader, with the whole file as HTML. After "Copy HTML file", diff between the clipboard (560px, 1440px) and the file finds no difference.
   • REST upload with a separate subject, preheader and text part: the clipboard (file) gains <head><title>Your weekly summary</title><meta name="preheader" content="Three things changed this week"></head>. The SDK parses it back to that subject and preheader (parse). The toast carries the text-part note.
   • Zero non-GET /api/ requests after any copy click.

   Screenshots (MockHog project, example.com repository, invented copy, no customer data). Narrow is a 560px window, about the scene of a 1280px window with the side panel open, as #503 used. Wide is 1440px.

   	Narrow (560px)	Wide (1440px)
   Page: split button	page	page
   Side menu open	menu	menu
   Toast, SDK-uploaded template	toast	toast
   Toast with the text-part note, REST template	toast	toast

   Committed story: Copy menu open.

   Gaps

   • No real posthog-node or REST upload into a running stack. The stack on this devbox serves the main checkout, not this worktree, as in Email templates: show "Managed by code" and the source file in the library #489, Email templates: read-only view of code-managed templates #492 and Edit with your agent: copy a prompt for a code-managed template's file #503. The browser round trip serves the exact upload fields instead. Upload stores those fields verbatim (template_uploads._email), so the page gets the same template. Ship stack A: edit a code-managed template with your agent #516 can run the real upload on the PR head.
   • Screenshots come from Storybook with the API mocked. The scene story was scratch and stays out of the commit.

   Calls made

   • Placement: the side action sits on EditWithAgentButton. It follows the precedent of workflow-publish in WorkflowSceneHeader.tsx (sideAction with a LemonMenuOverlay). MessageTemplateMenu.tsx and templateCopy.ts are unchanged: the overflow menu is not the button's side menu, and templateCopy is the Duplicate payload. The encoder got its own module.
   • The scanner mirrors the SDK's scanHead: comments and titles hide tags, the first title and preheader win, and a malformed tag stops the scan. The frontend can't import posthog-node, so about 40 lines repeat its rules. The vector table pins them to Think through the Elements tab PostHog/posthog#5312's head.
   • Liquid stays literal inside escaped values. Escaping applies only outside {{ … }} and {% … %}. A preheader whose Liquid holds " gets a single-quoted content='…'. Otherwise default: "there" would turn into " and break the Liquid when the HTML renders. When the Liquid holds both quote kinds, the encoder escapes everything, because the attribute can't hold both raw.
   • A changed subject is written whitespace-collapsed, which is what the SDK reads anyway.
   • A changed preheader rewrites its whole tag as <meta name="preheader" content="…">. Other attributes on that one tag go away.
   • "Blank" means empty or whitespace only. A tag that already holds exactly that value stays, so an SDK file with content="" copies back unchanged.
   • The SDK refuses a file without a <title> (template_missing_subject), so the missing-title cases are REST-shaped templates, not SDK files.
   • dropped_text_part is true when the saved text part is nonempty after trimming.
   • No pending state: the copy is a local clipboard write. A failure uses copyToClipboard's toasts, and the event fires only on success.
   • The toast is not a committed story. A clipboard write in the visual test runner isn't deterministic. The screenshots show the toast instead.
   • Boy scout: typegen replaced three any parameter types in Edit with your agent: copy a prompt for a code-managed template's file #503's selector types with their real types.
   • pnpm install --frozen-lockfile was needed in this worktree for Edit with your agent: copy a prompt for a code-managed template's file #503's new devDependencies. The lockfile is unchanged.
   • No review ran in this ticket. Ship stack A: edit a code-managed template with your agent #516 owns review.

   Follow-ups

   • Ship stack A: edit a code-managed template with your agent #516: run a real posthog-node upload from a file and a REST upload on the PR head, then diff the copy against the file.
   • Library card Duplicate still has no message template duplicated event (carried over from Edit with your agent: copy a prompt for a code-managed template's file #503).
   • If posthog-js changes parseTemplateFile before Think through the Elements tab PostHog/posthog#5312 merges, re-record the vector table with record-sdk-parse.ts against the new head.
8. Silthus

   closed this as completedon Oct 17, 2026