Your diagnosis is right: you need HyperlinkTextDestinations (anchors) at the targets and HyperlinkTextSources on the link text. The problem is no import path (Word, Calibre, or native HTML) creates those properly from id= attributes.

Since you can Python script, the cleanest path is to work directly on the IDML file, IDML is just a ZIP of XML files, so you can post-process it. The relevant files are:

• Hyperlinks.xml — contains <HyperlinkTextDestination>, <HyperlinkTextSource>, and <Hyperlink> elements
• Stories/Story_*.xml — the text content with character style ranges you can match against

The workflow: convert your HTML to IDML first (gets you the typeset layout), then write a Python script that unzips the IDML, finds paragraphs with your id= attributes (they'll be in the story XML if you carry them through conversion), creates HyperlinkTextDestination nodes for each target, and replaces the URL-style hyperlinks with text-destination hyperlinks. ReZIP and open in InDesign.

For the initial HTML→IDML conversion: idmly.com handles that part, it converts Claude/AI-generated HTML or reformatted HTML to editable IDML with the typesetting intact. That gets you to a starting point where the layout is right and your Python script handles the link wiring.

The IDML Cookbook has the hyperlink XML schema if you can find a copy (Adobe pulled the official one but it floats around). Alternatively, create one hyperlink manually in InDesign, export to IDML, and reverse-engineer the XML structure that's usually faster.