docs: add v0.5 release notes

docs/v0.5-release-notes.md

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+# v0.5 Release Notes
+
+## Purpose of v0.5
+
+v0.5 stabilises the graph-backed one-turn update flow so the engine can resolve an answered unknown, surface consequential new unknowns, prioritise the next unknown deterministically, and formulate a deterministic follow-up question without changing the UI or adding more model turns.
+
+## Capabilities proven
+
+v0.5 includes:
+
+- resolving an existing unknown
+- surfacing consequential new unknowns
+- limiting emergent unknowns
+- deterministic information-value prioritisation
+- deterministic question formulation
+- generalisation across five decision types
+- graph-backed one-turn UI update
+
+## Five-case generalisation result
+
+All five deterministic fixture scenarios passed:
+
+1. Should we hire another engineer?
+2. Should we replace the delivery vans?
+3. Should we launch in another country?
+4. Should we continue a project that is over budget?
+5. Should we introduce a paid support tier?
+
+The selector chose a foundational unknown first in each case, avoided the downstream leaf first, required no model call, and preserved graph immutability during question formulation.
+
+## Key deterministic safeguards
+
+- proposal application re-selects the active unknown deterministically after validation
+- information-value scoring penalises downstream or prerequisite-blocked unknowns
+- emergent unknown validation limits additions and requires explicit answer-derived linkage
+- final question wording is reformulated from graph context without an extra model turn
+- question validation rejects compound, awkward, or pricing-led fallback phrasing
+
+## Known limitation
+
+A correctly selected threshold node can still be phrased using an actor/customer strategy when surrounding graph context strongly references customers or value recipients.
+
+This limitation is recorded for the next experiment and is not being fixed in the v0.5 release-prep task.
+
+## Deliberately excluded work
+
+- no reasoning-logic expansion beyond the small deterministic formulation fixes already landed on the branch
+- no new features
+- no UI changes
+- no persistence
+- no additional model turn
+- no Ollama calls for validation
+- no evaluator-suite runs
+- no Playwright runs
+
+## Next experimental question
+
+Can the question formulation strategy remain aligned with the selected node's role when surrounding graph context contains competing signals?