my-pi/pi-permission-system/docs/retro/0129-extract-permission-session.md

issue, issue_title

issue	issue_title
129	refactor: extract PermissionSession class to encapsulate mutable session state

Retro: #129 — extract PermissionSession class

Final Retrospective (2026-05-08T02:30:00Z)

Session summary

Extracted a PermissionSession class that encapsulates all mutable session state (PermissionManager, SessionRules, cache keys, skill entries, runtime context) with operation-based methods replacing field access. Migrated all 4 handler files and 6 handler test files to use the new class, shrinking HandlerDeps from 18 to 7 fields. Released as v5.10.0 with 38 new unit tests and no behavioral change.

Observations

What went well

• SkillPermissionChecker interface extraction — the plan didn't anticipate that resolveSkillPromptEntries took a concrete PermissionManager type. Rather than using a cast, extracting a narrow SkillPermissionChecker interface in src/skill-prompt-sanitizer.ts let both PermissionManager and PermissionSession satisfy it structurally. This "narrow interface at the callee" pattern avoided adapter objects and should be the default approach for similar migrations.
• Phase collapse was efficient — the plan's strict 4-phase separation (build class → wire type → migrate handlers → cleanup) would have required updating every makeDeps factory twice. Collapsing phases 2–4 into handler-by-handler migration (each handler + its tests in one commit) was cleaner and produced smaller, reviewable diffs.
• Handler test simplification was dramatic — makeSession() factories went from 7 nested-mock fields with as unknown as SessionState["permissionManager"] casts to flat vi.fn() stubs. The tool-call-events.test.ts file shrank from 375 to 302 lines while preserving all test cases.

What caused friction (agent side)

1. premature-convergence — initial PermissionSession constructor followed the plan's "4 deps" signature literally (ExtensionPaths, SessionLogger, PermissionPrompterApi, ForwardingController), then added canPrompt()/prompt() methods before realizing the prompting surface doesn't belong on the session (it depends on ctx + subagent detection logic the session doesn't own). Resulted in writing and then deleting ~30 lines of prompting code, plus adding PermissionSessionRuntimeDeps as the actual 4th dep. Impact: ~10 minutes of rework across two edits.

2. missing-context — the lifecycle handler rewrite (src/handlers/lifecycle.ts) was written from memory rather than referencing the original. handleResourcesDiscover used an undeclared session variable and handleSessionShutdown called a non-existent session.clearStatus() method. Caught immediately on the next read, but the file had to be rewritten. Impact: one extra write cycle, no commit waste.

3. missing-context — vi.mock paths in the initial test file used ./src/ instead of ../src/. Tests run from tests/, so the relative paths were wrong. Caught on first test run. Impact: one extra edit, no rework.

4. missing-context — test mocks used shorthand SkillPromptEntry shapes like { name: "s", path: "/s", content: "c" } that passed Vitest (esbuild, no type checking) but failed tsc. The real type has 6 required fields (name, description, location, state, normalizedLocation, normalizedBaseDir). Fixed by adding a makeSkillEntry() helper. Impact: one extra commit fixup at the end, but could have been avoided by checking the SkillPromptEntry type before writing mock data.

5. wrong-abstraction — the plan proposed PermissionSession absorb canPrompt(ctx) and prompt(ctx, details), but these methods require isSubagentExecutionContext() and canResolveAskPermissionRequest() which depend on subagentSessionsDir and config — concerns the session shouldn't own. The correct boundary keeps prompting on HandlerDeps until #130 handler classes can own the ctx-capture pattern. Impact: plan deviation documented in the summary, no code waste beyond friction point #1.

What caused friction (user side)

• No friction observed. The user ran /plan-issue, /tdd-plan, and /ship-issue in sequence with no mid-session corrections needed. The autoformat hooks ran cleanly throughout.

Changes made

1. Created docs/retro/0129-extract-permission-session.md (this file).