feat: writes via chat — Reginald proposes, you approve inline (P4)

Completes "chat is the write-path" (decisions.md D1). Ask Reginald to re-estimate
or reprioritize an issue; it formulates a proposal, you approve it inline, and the
write runs through the same guarded apply_changes engine the Issue screen uses.
The model never writes — it proposes; the app owns approval + execution.

core (@commitea/core):
- propose_change tool declaration + REGINALD_SYSTEM updated ("never claim a change
  is applied; you propose, the human approves").
- proposalsFor(args, currentLabels, title): pure — builds the concrete, non-noop
  ChangeProposal(s) (change + label diff) for a propose_change request, dropping
  invalid/unchanged axes. ChangeProposal / ProposeChangeArgs types.

app:
- model bridge executes propose_change by planning against the issue's current
  labels (no write) and returns the proposals with the turn.
- useChat surfaces pending proposals + approve/dismiss; approve calls onApplyChange
  (AppShell's guarded handler → PUT + board/forecast refetch), dismiss leaves it.
- ChatPanel renders each proposal as a propose-approve card (diff + Approve/Dismiss).

Verified: 101 core tests green (4 proposalsFor added), desktop typecheck clean,
14 fixture e2e green. Gated live e2e against gemma-4-26b: "Set the estimate on #3
to est/5d" → Reginald proposes "est/2d → est/5d" as an inline card, says it's
*proposed* not done; Dismiss leaves the repo untouched. The approve→write path is
the #41 engine (separately verified change→revert).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/core/src/agent/agent-tools.ts

@@ -35,12 +35,30 @@ export const QUERY_PROJECT_TOOL: ToolDecl = {
   },
 }
 
-export const REGINALD_TOOLS: ToolDecl[] = [QUERY_PROJECT_TOOL]
+export const PROPOSE_CHANGE_TOOL: ToolDecl = {
+  name: 'propose_change',
+  description:
+    "Propose an estimate and/or priority change to an issue. This does NOT apply anything — it shows the " +
+    'human a diff to approve. Use it whenever the user asks to re-estimate or reprioritize. After calling it, ' +
+    "tell the user you've *proposed* the change for approval — never say it is done.",
+  parameters: {
+    type: 'object',
+    properties: {
+      issue: { type: 'number', description: 'the issue number to change' },
+      estimate: { type: 'string', enum: ['est/1d', 'est/2d', 'est/3d', 'est/5d', 'est/8d'] },
+      priority: { type: 'string', enum: ['p/1', 'p/2', 'p/3', 'p/4'] },
+    },
+    required: ['issue'],
+  },
+}
+
+export const REGINALD_TOOLS: ToolDecl[] = [QUERY_PROJECT_TOOL, PROPOSE_CHANGE_TOOL]
 
 export const REGINALD_SYSTEM = [
   'You are Reginald, the calm, dry project manager inside CommiTea — a tool that runs projects on Gitea.',
   'Call query_project to ground every answer in the real project; never invent issues, numbers, or dates.',
   'The scheduler and forecasts are deterministic code — report their output, do not recompute it.',
-  'Forecasts are ranges, never single dates. Refer to issues as #<number>.',
-  'Be brief and plain. A sentence or two is usually enough. No preamble, no bullet-point dumps.',
+  'To change an estimate or priority, call propose_change — it shows the human a diff to approve.',
+  'Never claim a change is applied; you propose, the human approves. Forecasts are ranges, never single dates.',
+  'Refer to issues as #<number>. Be brief and plain — a sentence or two. No preamble, no bullet dumps.',
 ].join(' ')