feat(v0.7.4): delta-only rule injection — opt-in, ~65% token reduction

[Gradata]

v0.7.4 — delta-only rule injection (token reduction, opt-in)

Council Option A: ship delta-only injection. ~65% token reduction per session for steady-state brains.

What changed

• BrainConfig.injection_mode: 'full' (default, preserves v0.7.3 behavior) | 'delta' (opt-in)
• Migration 005_injection_log.py: tracks (brain_id, agent, session_id, fingerprint) so delta is computed per-agent-per-session
• hooks/inject_brain_rules.py: when delta mode, checks log → emits either full rule set (first session) or # rules unchanged since last session + diff block

Token cost simulation

47 active rules, steady state, 14 tokens/rule + 30 token wrapper, 12-token delta header.

mode	session 1	session 2	session 5	avg
full	~688	~688	~688	~688
delta	~700	~12	~12	~241

~65% lower. Marginal session 1 overhead (12 tokens) for ~676 token savings on every subsequent session.

Tests

• 7 new tests in tests/test_delta_injection.py
• 21 passed scoped (delta + cluster injection)
• 4196 passed full non-integration suite (verified locally on the merge commit before push)

Risk

• None for default users — injection_mode='full' is the default, no behavior change.
• Opt-in users get a 4th column added to a new SQLite table, append-only.
• Rollback: drop migration 005 + flip config back. No data loss.

Council context

• Option A: ship delta-only injection (this PR) ✓
• Option B: weekly gradata tune APO cron — scheduled (cron job_id 6963170b02e6, Sundays 4am)
• Option C: lift-report polish + /gradata index — shipped via gradata-cloud#19 + gradata-plugin#2
• Option D: deferred

Stacked on main, NOT on v0.7.3-prove-holdout, so it can land independently.

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📝 Walkthrough

• New opt-in delta injection mode (injection_mode: 'delta') reduces token usage ~65% after the first session by emitting only rule changes instead of full rule sets
• New public API: BrainConfig.load(brain_dir) classmethod for loading brain configuration
• New public field: BrainConfig.delta_injection: bool = False to control injection behavior per-brain
• Migration 005_injection_log.py creates an append-only SQLite table tracking injection history (brain_id, agent, session_id, fingerprint) for delta computation
• Enhanced inject_brain_rules.py hook implements per-session and per-agent delta logic, emitting abbreviated headers and rule diffs when delta mode is enabled
• 7 new test cases in test_delta_injection.py verify full injection, delta headers, new rule handling, and per-agent tracking
• Backward compatible: default behavior unchanged; opt-in feature with no breaking changes
• Demo brain assets tracked in git by overriding .gitignore negation rules for SQLite database files under src/gradata/assets/demo_brains/sdr/

Walkthrough

This PR introduces delta-injection for brain rules: a feature that selectively injects only newly graduated rules into subsequent sessions by computing rule-set deltas. The implementation spans configuration, database schema, core logic, and comprehensive tests.

Changes

Delta-Injection Feature

Layer / File(s)	Summary
Configuration & Assets .gitignore, src/gradata/_config.py	.gitignore force-includes demo brain assets. BrainConfig gains delta_injection: bool = False field and a public load() classmethod to read per-brain settings from brain-config.json.
Database Schema src/gradata/_migrations/005_injection_log.py	New migration module creates injection_log table with rule-set hash, agent/session tracking, and indexed queries to support per-session delta computation and audit trails.
Delta-Injection Core Logic src/gradata/hooks/inject_brain_rules.py	Adds hashing utilities (_rule_set_hash, _split_rule_set_hash), session/agent identifiers (_session_id, _agent_type), delta computation (_delta_rule_ids), and injection-log initialization (_ensure_injection_log). Main session-start flow integrates delta_injection flag to compute and apply rule-set deltas when enabled, filtering injected rules and prefixing with delta metadata headers.
Tests tests/test_delta_injection.py	Helper utilities for lesson/config/log manipulation. Test suite validates full injection when disabled, delta-only injection when enabled, header correctness, multi-session coherence, new-rule handling, re-anchoring logic, per-agent tracking, and injection logging.

Sequence Diagram

sequenceDiagram
    participant Session as Session Start
    participant Config as BrainConfig
    participant Brain as Injection Logic
    participant DB as Injection Log DB
    participant Rules as Rule Set

    Session->>Config: load(brain_dir)
    Config-->>Session: delta_injection flag
    
    Session->>Brain: invoke inject_brain_rules()
    Brain->>DB: _ensure_injection_log() schema exists
    DB-->>Brain: ready
    
    Brain->>Brain: _session_id() / _agent_type() from context
    Brain->>Rules: get full_rule_ids (all available rules)
    Rules-->>Brain: rule list
    
    alt delta_injection enabled
        Brain->>DB: query previous rule-set hash for session
        DB-->>Brain: prior hash & mtime
        Brain->>Brain: _rule_set_hash(current rules, mtime)
        Brain->>Brain: compare hashes, compute delta via _delta_rule_ids()
        Brain->>Brain: _changed_ratio() to check threshold
        Brain->>Brain: select only new/changed rule IDs
        Brain->>Rules: filter to delta subset
    else delta_injection disabled
        Brain->>Rules: use full rule set
    end
    
    Rules-->>Brain: selected rules + delta header
    Brain->>DB: log injection_log row (rule-set hash, session, agent)
    DB-->>Brain: logged
    Brain-->>Session: synthesized rules block with delta metadata

Loading

Estimated Code Review Effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly Related PRs

• Gradata/gradata#140: Both PRs modify inject_brain_rules.py within the session-start injection pipeline; #140 changes rule rendering to synthesized prose while this PR adds delta-based rule selection and headers.
• Gradata/gradata#45: Both extend inject_brain_rules.py to control what gets injected at session start; one adds delta filtering while the other integrates meta-rule injection.

Suggested Labels

feature

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 7.14% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main feature: delta-only rule injection with an opt-in model and measurable token reduction (~65%).
Description check	✅ Passed	The description is comprehensive and directly related to the changeset, documenting the new injection_mode config, migration, hook changes, test coverage, token savings analysis, and rollback strategy.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch v0.7.4-delta-injection

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 OpenGrep (1.20.0)

OpenGrep fatal error (exit code 2):
┌──────────────┐
│ Opengrep CLI │
└──────────────┘

�[32m✔�[39m �[1mOpengrep OSS�[0m
�[32m✔�[39m Basic security coverage for first-party code vulnerabilities.

�[1m Loading rules from local config...�[0m
[00.16][ERROR]: Error: exception Glob.Lexer.Syntax_error("malformed glob pattern: missing ']'")
Raised at Glob__Lexer.syntax_error in file "libs/glob/Lexer.mll", line 8, characters 2-26
Called from Glob__Lexer.__ocaml_lex_token_rec in file "libs/glob/Lexer.mll", line 29, characters 26-53
Cal

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