Title#

fix: replan/restart must invalidate cached plan and PR association

Problem#

When /agent replan or /agent restart fires, stale plan artefacts and PR associations were reused on the next run. replan did not clear plan files; restart did not clear prNumber/prBranch at all.

Task / Link#

Closes #234

Changes#

• Added replanAttempt integer column (default 0) to TaskEntity
• Added resetForReplan() to TaskStateService: resets all phases, nullifies prNumber/prBranch, increments replanAttempt
• Added clearPlanArtefacts(taskDir) to ArtefactsService: removes plan.md, context.json, prd.json from the plan directory
• Updated DirectiveService replan handler: uses resetForReplan(), calls clearPlanArtefacts(), records replan_attempt telemetry, posts superseded comment before closing PR
• Updated DirectiveService restart handler: clears prNumber/prBranch, closes open PR with superseded comment
• Added unit tests covering all new behaviours and no-op edge cases

Notes#

• clearPlanArtefacts is a no-op when the plan directory is absent (idempotent)
• restart previously did not touch PR state; this is a deliberate behavioural change required by the issue
• TypeORM synchronize mode handles the new column; no explicit migration needed

Testing#

• Unit tests: resetForReplan() clears PR fields and increments counter; replan clears plan artefacts; restart clears PR state; replan_attempt telemetry recorded; no-op with no prior state
• npm run lint — passes (pre-existing ws-gateway errors unrelated)
• npm run test — 675 tests pass, 1 pre-existing failure in ws-gateway (missing @nestjs/websockets dev dep)