W-19857466: preserve accessToken before calling ai-agent APIs

[EstebanRomero84]

What does this PR do?

Preserve accessToken before calling ai-agent APIs.

What issues does this PR fix or reference?

@W-19857466@

[WillieRuemmele]

QA Notes

---

✅ : success with valid .agent file
⚠️ : without hack, CANNOT publish new version, known limiation
✅ : retrieved new changes, added target field to meta, incremented version

 ➜  SF_TEST_API=true sf agent publish authoring-bundle                              
 ›   Warning: @salesforce/plugin-agent is a linked ESM module and cannot be auto-transpiled. Existing
 ›    compiled source will be used instead.
? API name of the authoring bundle to publish willie

 ──────────────── Publishing Agent ────────────────

 ✔ Validate Bundle 3.31s
 ✔ Publish Agent 11.67s
 ✔ Retrieve Metadata 2.18s

 Agent Name: willie
 Elapsed Time: 17.18s

✅ : invalid agent file compilation errors shown

 ➜  SF_TEST_API=true sf agent publish authoring-bundle
 ›   Warning: @salesforce/plugin-agent is a linked ESM module and cannot be auto-transpiled. Existing
 ›    compiled source will be used instead.
? API name of the authoring bundle to publish willie

 ──────────────── Publishing Agent ────────────────

 ✘ Validate Bundle 1.11s
 ◼ Publish Agent
 ◼ Retrieve Metadata

 Agent Name: willie
 Elapsed Time: 1.12s

Error (2): Failed to publish agent with the following errors:
SyntaxError: Unexpected 'instctions' [Ln 2, Col 2]