docs(specs): kick off authorization-obligations (brief + requirements, unapproved)

Absence bugs as obligations rather than flows: obligated operations and
discharger kinds as closed facts, obligation shapes learned from trusted
pairs, the application's policy recovered from sibling-handler
consistency and an optional declared policy file, path-aware evaluation
with a function-local degraded mode, honest rungs below proof, an
`obligations` improve lever under the holdout gate. Depends on
reachability-flow-model and guard-dominance-regime; the roadmap marks
reachability as the critical path for two consumers.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG

.kiro/steering/roadmap.md

@@ -85,6 +85,7 @@ sast: java-sqli moved MISS→LEAK (coverage counted on both sides; the fixed twi
 - [x] real-world-vfc-slice -- Harvest reviewed function-level vuln/fix pairs from large projects (Firefox/gecko-dev, Chromium, OpenSSL, …) as an honesty slice. Seed is testable (`ousast pairs --slice vfc`). Dependencies: none. **Closed 2026-09-04, superseded by pair-corpus-honesty on the corpus/scorer plane.**
 - [x] pair-corpus-honesty -- Scorer counts coverage and matches by function; labels carry mechanism/provenance/split/known_limit; harvest anchors at the declarator with line-range and hunk modes; sast hygiene; new slices `vibe-py` (Real-Vuln-Benchmark), `vfc-js` (SecBench.js fix commits), `agent-vfc` (agent-trailer fixes); deterministic provenance fingerprint; per-profile improve acceptance; review tiers and pointer slices (amendment). Dependencies: none (supersedes real-world-vfc-slice). **Completed 2026-09-05 (11 review rounds).**
 - [x] corpus-seeded-mechanisms -- Every seeded or reviewed pair becomes a mechanism record (source shape, sink shape, guard the fix added); structural variant search over the scanned tree proposes matches as `variant` findings that the overlay and sandbox verify; leave-one-out recall on the pair corpus is the corpus's own detection rate; the improve loop gains a recall-raising `mechanisms` lever under the per-profile holdout gate. Principle: recall first under a false-positive ceiling, per profile. Dependencies: pair-corpus-honesty (tiers, pointer slices). **Completed 2026-09-05 (6 review rounds).**
-- [ ] reachability-flow-model -- Name-resolved call graph over `FunctionIR`; per-function taint summaries composed along the graph into path records; graph reachability drives rank, map, worth-fixing; hunter gets `path_context` and hunter findings with a locatable sink become sandbox candidates; closed-kind fact oracle with candidate cache; `facts` improve lever under the per-profile gate; fix points ranked by reachable risk removed. Dependencies: pair-corpus-honesty
+- [ ] reachability-flow-model -- Name-resolved call graph over `FunctionIR`; per-function taint summaries composed along the graph into path records; graph reachability drives rank, map, worth-fixing; hunter gets `path_context` and hunter findings with a locatable sink become sandbox candidates; closed-kind fact oracle with candidate cache; `facts` improve lever under the per-profile gate; fix points ranked by reachable risk removed. Dependencies: pair-corpus-honesty **Critical path: two consumers wait on it (guard-dominance-regime and authorization-obligations).**
 - [ ] overlay-ir-completeness -- Shared CST walker completeness (C `init_declarator`, lvalue paths for field stores, per-grammar literal kinds, local ERROR-node tolerance, multi-line C/C++ declarators the walker names `<anon>` and `functions.py`'s one-line rescue cannot name: `chromium-cve-2022-2162`, `openssl-cve-2025-69421`; a Scorer-side multi-line-aware rescue is the cheaper alternative) plus Python parity with stdlib ast (f-string constness, augmented assignment, kwargs); injection-regime facts: container/transformer taint, `weak_literals` consulted, parameter sources off for injection. Measured on sast and vibe-py. Dependencies: pair-corpus-honesty
+- [ ] authorization-obligations -- Absence bugs as obligations, not flows: obligated operations (protected read/write, privileged action, security setting) and discharger kinds (path guard, identity constraint from authenticated context, ownership check, non-permissive value) as closed facts; obligation shapes learned from trusted pairs; the application's policy recovered from sibling-handler consistency and an optional declared, versioned policy file; violations evaluated on the path (function-local degraded mode without it) with `consistency_violation` / `declared_policy_violation` rungs below proof; `obligations` improve lever under the holdout gate; the hunter adjudicates intent only. Measured leave-one-out on the vibe-py and agent-vfc absence pairs (today 0 detected; 15 of 29 agent-vfc rows). Dependencies: reachability-flow-model, guard-dominance-regime, corpus-seeded-mechanisms. **Requirements drafted 2026-09-05, unapproved.**
 - [ ] guard-dominance-regime -- Guard and Use IR records; guard dominance by nesting or early exit; memory sinks (memcpy/malloc/deref) with operand roles, nullable callees, out-param transformers, fixed-array capacity; same regime applied to web absence bugs (route auth guard, identity from auth context). Consumes path records. Measured on vfc, vfc-js, agent-vfc. Dependencies: reachability-flow-model, overlay-ir-completeness