Five primitives I exercised end-to-end on world-model-mcp's own repo

Saravanan Jaichandaran — Thu, 21 May 2026 05:36:21 +0000

I shipped four releases of world-model-mcp in twelve days. v0.6.1 to v0.7.2. The pitch is "AI coding agents lose context across compaction, repeat the same mistakes, and hallucinate APIs that do not exist." Before I write more about it I wanted to demonstrate the primitives on a real codebase, with real outputs, not screenshots someone has to take my word for.

The codebase is the project's own repo. I ran python -m world_model_server.cli setup (it auto-seeded 598 entities from the source), then ran scripts/demo_seed.py which inserts the small set of constraints, facts, and a compaction audit row that real PostToolUse / record_correction hook activity would write organically over one to two weeks of development with Claude Code installed.

Every output block below is verbatim from the actual SQLite database after running the actual command. You can reproduce every output here by cloning the repo, running python -m world_model_server.cli setup, then python scripts/demo_seed.py. The script is idempotent and supports --dry-run and --reset.

Install: pip install world-model-mcp. Source: github.com/SaravananJaichandar/world-model-mcp.

1. A learned constraint denying an edit at the PreToolUse boundary

When a developer corrects the agent (rewrites console.log to logger.debug), the PostToolUse hook records the diff and infers a rule. Once that rule's violation count crosses the hard-threshold (severity=error, count ≥ 3), the next attempt is denied at PreToolUse before the tool runs.

The constraint as the graph stores it:
{
"rule_name": "no-console-log",
"severity": "error",
"violation_count": 5,
"description": "Use logger.debug() not console.log() in TypeScript source. Production logs route through pino; console.log bypasses formatting and breaks downstream parsers.",
"file_pattern": "*.ts",
"examples": [
{"incorrect": "console.log", "correct": "logger.debug"}
]
}
The PreToolUse hook's actual JSON response when an edit containing console.log reaches it:
{
"hookSpecificOutput": {
"hookEventName": "PreToolUse",
"permissionDecision": "deny",
"permissionDecisionReason": "Hard constraint violation: no-console-log (Use logger.debug() not console.log() in TypeScript source. Production logs route through pino; console.log bypasses formatting and breaks downstream parsers.). Violated 5 times previously."
},
"violations": [
{
"rule": "no-console-log",
"severity": "error",
"violation_count": 5,
"is_hard": true,
"is_defer": false
}
]
}
Rules in CLAUDE.md or AGENTS.md are advisory and the model treats them as suggestions. Rules with a violation count and an enforcement boundary at the edit step are binding. Both have the same source — a developer correcting the agent — but very different effect.

2. A regression warning that flags edits to a file with a recorded bug fix

get_related_bugs walks decision traces and prior bug-fix facts. When validate_change runs on a file with a recorded fix, the related-bugs query surfaces the prior fix and flags the proposed change.

The project has a bug fix on file world_model_server/knowledge_graph.py:120-135 for content-hash backfill (the migration logic must run on every initialize(), not just when the column is created). I proposed a refactor that removed the backfill loop and ran the related-bugs check:
{
"risk_score": 0.6,
"bugs": [
{
"bug_id": "12457e2a-5638-46ec-a9df-02fe13b9c104",
"description": "Bug fix: NULL content_hash backfill must run on every initialize() to cover post-migration inserts. Earlier code only backfilled when the column was created, which left merge_from rows un-hashed and broke dedup.",
"fixed_at": "2026-05-10T10:17:51.737046",
"critical_regions": [
{"file": "world_model_server/knowledge_graph.py", "lines": "120-135"}
]
}
],
"warnings": [
"Lines 120-135 preserve fix for 12457e2a-5638-46ec-a9df-02fe13b9c104: Bug fix: NULL content_hash backfill must run on every initialize() to cover post-migration inserts. Earlier code only backfilled when the column was created, which left merge_from rows un-hashed and broke dedup."
]
}
The risk score is 0.6 because the proposed change touched a critical region without re-implementing the fix. The warning text quotes the original bug description directly so the agent (or the human) can see why the region matters, not just that it does.

3. A contradiction resolved by confidence + source-count weighting
The temporal layer assigns each fact a confidence score, a source_count, and a valid_at timestamp. When two facts about the same entity disagree, find_contradictions surfaces them with both sides' metadata, and resolve_contradiction picks a winner using the strategy you set.

Two facts both pointing at the same entity (http_transport_port):
{
"fact_a_id": "e4b2ff84-8c23-4de5-aa9e-8bbb045a4ed5",
"fact_b_id": "7fe854f9-d64a-4304-b43a-7d1b126c6ebb",
"fact_a_text": "HTTP transport listen port default is 8080",
"fact_b_text": "HTTP transport listen port default is 8765",
"similarity_score": 0.929,
"both_valid": true,
"reason": "same entity, similar text",
"confidence_a": 0.7,
"confidence_b": 0.95,
"source_count_a": 1,
"source_count_b": 3
}
resolve_contradiction(strategy="auto") picks the strategy with the largest signal gap. Here source count differs 3:1, so it picks keep_most_sources:
{
"strategy": "keep_most_sources",
"winner_id": "7fe854f9-d64a-4304-b43a-7d1b126c6ebb",
"loser_id": "e4b2ff84-8c23-4de5-aa9e-8bbb045a4ed5",
"resolved_at": "2026-05-21T10:24:16.287368"
}
The loser is updated in place:
{
"id": "e4b2ff84-8c23-4de5-aa9e-8bbb045a4ed5",
"fact_text": "HTTP transport listen port default is 8080",
"status": "superseded",
"invalid_at": "2026-05-21T10:24:16.285184",
"confidence": 0.7
}

Queries that ask "what's true now?" silently skip the superseded fact. Queries that ask "what was true on 2026-05-18?" still see it. That's what the temporal layer earns.

4. The PostCompact injection bundle
v0.7.0 added a PostCompact hook that re-injects the top constraints and recent canonical facts after the agent's context is compacted. The bundle is small (configurable, default ~10 constraints + 10 facts) and prioritized.

The actual bundle returned by get_injection_context(event_type="PostCompact", max_constraints=5, max_facts=5):

Active constraints (top by violation count)

no-console-log: Use logger.debug() not console.log() in TypeScript source. Production logs route through pino; console.log bypasses formatting and breaks downstream parsers. (violated 5x)
check-twine-before-tag: Run python3 -m twine check dist/* before tagging. Catches PyPI metadata errors before the tag is pushed; saves a retraction. (violated 5x)
tag-before-upload: Always run git tag + git push --tags before twine upload. PyPI is permanent; an untagged upload pins a wheel to no git ref. (violated 2x)

Recent canonical facts

Never run twine upload before git tag. Always tag, push, then upload to PyPI so the published wheel maps to a real git ref.
Cursor hooks.json uses object-keyed schema with version: 1 (integer), preToolUse / preCompact / beforeSubmitPrompt event names, failClosed (not fail_open), timeout in seconds.
PostCompact and UserPromptSubmit hooks emit additionalContext to splice constraints + recent facts back into agent context after compaction.
HTTP transport defaults to port 8765 in Dockerfile.http; do not change without updating docs/deployment/mcp-tunnel.md and docker-compose.yml together.
BetaAbstractMemoryTool subclass lives at world_model_server/memory_backend.py; required by the Anthropic SDK Managed Agents memory path.

That bundle is what gets spliced into the agent's working context as additionalContext after a compaction event. The same query also runs on UserPromptSubmit, biased toward whatever the user just asked about.

The compaction audit log records what happened, queryable via the CLI:

$ world-model audit-compactions --limit 5
1 compaction audit rows
2026-05-21T10:38:01.606771 session=demo-session-1 pre=84320
post=22150 facts_injected=10 constraints_injected=3 event=PostCompact
pre=84320, post=22150 — the compaction dropped ~62k tokens of context. The injection put 10 facts + 3 constraints back. The audit row exists so a human can later answer "what did the agent see vs what did it lose."

5. A defer decision that pauses a headless agent

v0.7.0 added a defer enforcement tier between deny and warn. Warning-severity violations with violation_count ≥ 5 return permissionDecision: "defer" when the client advertises support, so headless agents pause instead of silently passing or hard-blocking. Clients that do not advertise support fall back to ask automatically.

I have a check-twine-before-tag constraint with violation_count=5, severity=warning. When a Bash tool input matches it, the hook returns:
{
"hookSpecificOutput": {
"hookEventName": "PreToolUse",
"permissionDecision": "defer",
"permissionDecisionReason": "Recurring warning-level violations (check-twine-before-tag). Headless agents should pause for confirmation."
}
}
Same payload, same constraint, but with supports_defer: false in the request — fall back to ask:
{
"hookSpecificOutput": {
"hookEventName": "PreToolUse",
"permissionDecision": "ask",
"permissionDecisionReason": "Recurring warning-level violations (check-twine-before-tag). Headless agents should pause for confirmation."
}
}
The defer tier exists because the binary deny / warn choice forces you to either be too strict or too permissive. Recurring warnings that don't rise to error-level should pause for a human, not block, not pass.

What this means if you are building agents

The reason this works is not that the tool is clever. It is that the substrate — a temporal knowledge graph with facts, constraints, contradictions, and decision traces — captures the right shape of information.

Plain markdown rules in CLAUDE.md cannot answer:

How many times has this rule been violated?
Which fact is true now vs three sessions ago?
Which constraints should I re-inject after compaction?
Which prior fix does this proposed change risk re-introducing?

A graph can. The cost is one MCP server, ~2,000 lines of Python, and a SQLite database that sits at ~155 KB empty (mine grew to about 2 MB after running this exercise plus the auto-seed). The payoff is a memory layer that survives compaction, enforces at the edit boundary, and tracks evidence chains back to the source.

If you are building anything with Claude Code, Cursor, or any harness that supports MCP + hooks:

pip install world-model-mcp
cd /your/project
python -m world_model_server.cli setup

For Claude Managed Agents with self-hosted sandboxes (where Anthropic's built-in Memory primitive is not yet supported), v0.7.2 added streamable HTTP transport so the same 25 MCP tools also work behind an MCP tunnel.

Source: github.com/SaravananJaichandar/world-model-mcp.

If world-model-mcp helped you, star the repo or open an issue with what worked or didn't. I read every one.

DEV Community: Saravanan Jaichandaran

Five primitives I exercised end-to-end on world-model-mcp's own repo

Active constraints (top by violation count)

Recent canonical facts