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Internal Link Coherence

File: src/cofounder_agent/modules/content/internal_link_coherence.py Tested by: src/cofounder_agent/tests/unit/services/test_internal_link_coherence.py Last reviewed: 2026-04-30

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What it does

InternalLinkCoherenceFilter is the gatekeeper between the candidate-collection step of the internal-link recommender and the point where candidates are rendered into the writer prompt. It exists to fix two specific failure modes (GH-88) that pre-filter recommenders hit:

1. Off-topic neighbours. Embedding similarity put the CadQuery post in the “related” list for any “engineering fundamentals” topic, so the writer pinned Consider exploring CadQuery calls-to- action on asyncio and AI-engineering posts.
2. Single-target spam. With no cap, the same target slug could be suggested as “related” on an unbounded number of posts.

The filter applies two guards per candidate, in order: (1) tag coherence — source and target must share at least one normalized topic tag; (2) single-target cap — no candidate may already have N+ inbound internal links from published posts. Rejections are recorded on the original LinkCandidate.rejection_reason so audit logging and debug dumps can explain why a candidate was filtered. The filter is best-effort: when the DB is unreachable or queries fail, it logs and lets candidates through unfiltered, on the “a half-broken recommender is still better than no recommender” principle. Both guards are configurable and default to ON.

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Public API

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Top-level helpers

• normalize_tag_set(tags) -> set[str] — folds a heterogeneous list (strings, dicts with slug/name, mixed-case names) into a canonical tags.slug-format set so set-overlap is meaningful.
• await get_tag_slugs_for_post(pool, *, post_id=None, slug=None) -> set[str] — looks up a target post’s tag slugs by either post_id (UUID string) or slug. Returns set() when the pool is missing, neither identifier was given, or the query fails.
• await count_inbound_links_to_slug(pool, slug) -> int — counts published posts whose body contains a /posts/<slug> link. Uses ILIKE for the prefilter and a regex post-filter to avoid false positives where one slug is a prefix of another.

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LinkCandidate dataclass

Fields: slug (required), title (required), post_id (optional — the ILIKE-based collection path in ResearchService only has title+slug), similarity, tag_slugs, inbound_count, rejection_reason, metadata. The filter hydrates tag_slugs and inbound_count lazily — callers can pre-populate them to skip those DB calls.

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InternalLinkCoherenceFilter

• InternalLinkCoherenceFilter(*, pool=None, tag_coherence_required=None, single_target_cap=None, cap_enabled=None) — constructor. Each kwarg defaults to its app_settings value (or to the strict-by-default constants if the setting is unset).
• await filt.filter_candidates(*, source_tags, candidates) -> list[LinkCandidate] — main entry. Returns the survivors in input order. Rejected candidates are NOT returned but their rejection_reason is set on the original object so callers retaining the full list can introspect.
• filt.tags_overlap(source, target) -> bool (staticmethod) — pure set-intersection check after normalize_tag_set.
• filt.under_cap(inbound_count) -> bool — True if the cap is disabled OR the count is strictly below the cap.

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Key behaviors / invariants

• Strict by default. Both guards default to enabled. To loosen, set internal_link_tag_coherence_required=false or internal_link_single_target_cap_enabled=false in app_settings.
• No source tags = reject everything when tag-coherence is on. This is deliberate: silently passing every candidate when the source has no tags is exactly the bug the gate exists to prevent. Matches the project-wide “no silent defaults” stance.
• Untagged targets are rejected when tag-coherence is on. Legacy posts created before the post_tags migration land here. There’s no “fall back to category match” path — fix by tagging the post.
• Tag normalization is one-way. normalize_tag_set lower-cases, slugifies (re.sub(r"[^a-z0-9]+", "-", ...)) and strips edge dashes. Inputs can be names ("3D Modeling"), slugs ("3d-modeling"), or dicts with slug/name keys — all collapse to the same value.
• Single-target cap is lazy. count_inbound_links_to_slug doesn’t run unless a candidate has cleared the tag check, so rejected-by-tag candidates don’t waste a query.
• Inbound count is approximate but skewed safe. The slug-prefix edge case (e.g. foo matching inside foo-bar) over-counts, which triggers the cap slightly sooner than necessary. That’s the safer direction — recommender errs toward variety.
• DB failure = fail open per call. Each helper catches its own exceptions and returns set() / 0. The filter then sees an unfiltered candidate and either rejects it (if tag-coherence requires tags it can’t fetch) or passes it through (if the cap query fails — count defaults to 0).

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Configuration

• internal_link_tag_coherence_required (default true) — toggles the tag-overlap requirement.
• internal_link_single_target_cap (default 3) — max inbound internal links per target slug. Strict less-than comparison.
• internal_link_single_target_cap_enabled (default true) — toggles the cap enforcement.

All three are read via services.site_config.site_config.get with the constructor kwargs as overrides for tests / one-off invocations. Reads are wrapped in try/except — broken site_config falls through to the strict defaults, never raises.

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Dependencies

• Reads from:
  • posts + post_tags + tags tables — for target tag lookup via get_tag_slugs_for_post.
  • posts.content — ILIKE scan for inbound link counting via count_inbound_links_to_slug (filtered to status='published').
  • services.site_config.site_config — for the three tunable settings.
• Writes to: nothing. Pure read-only filter.
• External APIs: none.
• Callers:
  • services.research_context.build_rag_context — wraps the pgvector-based candidate list. Pulls source_tags from the content task and applies the filter before rendering the “RELATED POSTS WE’VE PUBLISHED” prompt block.
  • services.research_service (mentioned in the module docstring as the ILIKE-based path that triggered the original GH-88 bug — confirm in code if you’re refactoring; today only research_context.py actually imports the filter).

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Failure modes

• DB pool is None — both helpers return their empty/zero defaults; the filter rejects all candidates if tag-coherence is on (target tags can’t be fetched), or passes them through if it’s off.
• Tag lookup query fails — get_tag_slugs_for_post catches and returns set(). Same downstream behavior as “no tags.”
• Inbound count query fails — count_inbound_links_to_slug catches and returns 0, so the cap check passes. Conservative failure mode.
• filter_candidates itself raises (shouldn’t, but): caller in research_context catches and logs "Internal-link coherence filter failed" via logger.exception — the candidate list falls through un-rendered (no RAG block in the prompt for that draft).
• Cap fires too aggressively — usually a slug-prefix collision (one slug being a substring of another with a - boundary). The regex post-filter is supposed to catch this; if it doesn’t, file a test case with the offending slug pair.

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Common ops

• Loosen the cap globally:
  poindexter settings set internal_link_single_target_cap 5
  
• Disable the cap entirely (debug):
  poindexter settings set internal_link_single_target_cap_enabled false
  
• Disable tag-coherence (NOT recommended):
  poindexter settings set internal_link_tag_coherence_required false
  
• Find slugs that hit the cap recently: grep production logs for [LINK_COHERENCE] cap reached for <slug>: N inbound (cap=...).
• Audit a specific candidate: construct one and run it through the filter directly:
  from modules.content.internal_link_coherence import (
      InternalLinkCoherenceFilter, LinkCandidate
  )
  cand = LinkCandidate(slug="foo", title="Foo")
  survivors = await InternalLinkCoherenceFilter(pool=pool).filter_candidates(
      source_tags=["python", "asyncio"],
      candidates=[cand],
  )
  print(cand.rejection_reason or "passed")
  

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See also

• services.research_context.build_rag_context — the call site that wires the filter into the RAG path.
• docs/architecture/services/research-and-web-research.md — the research stage pair this filter sits between (candidate collection ↔ writer prompt).
• docs/architecture/services/content_router_service.md — the pipeline whose RAG block is what this filter actually constrains.