fix(retry): promote free-tier action message to shared const

Cubic flagged that the inline literal change in retry.ts:87 ("Subscribe
to OpenCode Go ... $5/month" -> "Free usage limit reached on this
provider.") broke retry.test.ts:257 which asserted on the upstream
literal byte-for-byte.

Right fix: shared const, so test and impl reference one symbol and
future BrowserCode-side neutral edits don't need synchronized test
updates. Mirrors the existing GO_UPSELL_MESSAGE / GO_UPSELL_URL
pattern. Added FREE_TIER_ACTION_MESSAGE; test now uses
SessionRetry.FREE_TIER_ACTION_MESSAGE.

The schema-decoding.test.ts inline literal stays — that's a
schema-shape decode/encode round-trip with arbitrary string values,
not an assertion on retry.ts behavior.

Verified: bun typecheck 6/6 clean; retry.test.ts 31/31 pass;
schema-decoding.test.ts 25/25 pass.

Author: bcode

packages/opencode/src/session/retry.ts

@@ -11,6 +11,12 @@ export type Err = ReturnType<NamedError["toObject"]>
 // literal equality; leaving these as neutral values keeps the upsell UI dark.
 export const GO_UPSELL_MESSAGE = "Free usage exceeded"
 export const GO_UPSELL_URL = ""
+// Body shown if the TUI ever rendered the action card. Never visible in
+// practice because GO_UPSELL_URL is empty -> DialogRetryAction skips the
+// GO-treatment branch. Kept as an exported const so tests and downstream
+// consumers reference one symbol and don't drift on future BrowserCode-side
+// neutralization edits.
+export const FREE_TIER_ACTION_MESSAGE = "Free usage limit reached on this provider."
 export type RetryReason = "free_tier_limit" | "account_rate_limit" | (string & {})
 
 export type Retryable = {
@@ -82,9 +88,7 @@ export function retryable(error: Err, provider: string) {
           reason: "free_tier_limit",
           provider,
           title: "Free limit reached",
-          // Sentinel message; never surfaces because GO_UPSELL_URL is empty so the
-          // TUI retry-action dialog skips the OpenCode-Go upsell treatment.
-          message: "Free usage limit reached on this provider.",
+          message: FREE_TIER_ACTION_MESSAGE,
           label: "subscribe",
           link: GO_UPSELL_URL,
         },

packages/opencode/test/session/retry.test.ts

@@ -254,7 +254,7 @@ describe("session.retry.retryable", () => {
         reason: "free_tier_limit",
         provider: "opencode",
         title: "Free limit reached",
-        message: "Subscribe to OpenCode Go for reliable access to the best open-source models, starting at $5/month.",
+        message: SessionRetry.FREE_TIER_ACTION_MESSAGE,
         label: "subscribe",
         link: SessionRetry.GO_UPSELL_URL,
       },